uhd: add dependency on ncurses

* when it's not found in target sysroots it's trying to use native one
  | cd uhd/1_3.5.3-r3.0/git/host/build/examples && sysroots/x86_64-linux/usr/bin/cmake -E cmake_link_script CMakeFiles/rx_ascii_art_dft.dir/link.txt --verbose=1
  | sysroots/x86_64-linux/usr/bin/armv5te-oe-linux-gnueabi/arm-oe-linux-gnueabi-g++    -march=armv5te -marm -mthumb-interwork  --sysroot=sysroots/qemuarm  -O2 -pipe -g -feliminate-unused-debug-types -fpermissive -fvisibility-inlines-hidden -fpermissive -O2 -pipe -g -feliminate-unused-debug-types  -O2 -pipe -g -feliminate-unused-debug-types -fpermissive -fvisibility-inlines-hidden -DNDEBUG  -march=armv5te -marm -mthumb-interwork  --sysroot=sysroots/qemuarm  -O2 -pipe -g -feliminate-unused-debug-types -fpermissive -fvisibility-inlines-hidden -Wl,-O1 -Wl,--hash-style=gnu -Wl,--as-needed  -Wl,-O1 -Wl,--hash-style=gnu -Wl,--as-needed CMakeFiles/rx_ascii_art_dft.dir/rx_ascii_art_dft.cpp.o  -o rx_ascii_art_dft
  -Lsysroots/x86_64-linux/usr/lib -rdynamic ../lib/libuhd.so.003.005 -lcurses sysroots/x86_64-linux/usr/lib/libform.so -lboost_date_time-mt -lboost_filesystem-mt -lboost_program_options-mt -lboost_regex-mt -lboost_system-mt -lboost_thread-mt -lboost_unit_test_framework -lrt -lusb-1.0 -lpthread -ldl -Wl,-rpath,uhd/1_3.5.3-r3.0/git/host/build/lib:sysroots/x86_64-linux/usr/lib:
  | sysroots/x86_64-linux/usr/libexec/armv5te-oe-linux-gnueabi/gcc/arm-oe-linux-gnueabi/4.8.1/ld: error: sysroots/x86_64-linux/usr/lib/libform.so: incompatible target
  | sysroots/x86_64-linux/usr/libexec/armv5te-oe-linux-gnueabi/gcc/arm-oe-linux-gnueabi/4.8.1/ld: warning: skipping incompatible sysroots/x86_64-linux/usr/lib/libncurses.so.5 while searching for libncurses.so.5
  | sysroots/x86_64-linux/usr/libexec/armv5te-oe-linux-gnueabi/gcc/arm-oe-linux-gnueabi/4.8.1/ld: warning: skipping incompatible sysroots/x86_64-linux/usr/lib/libncurses.so.5 while searching for libncurses.so.5
  | sysroots/x86_64-linux/usr/libexec/armv5te-oe-linux-gnueabi/gcc/arm-oe-linux-gnueabi/4.8.1/ld: error: cannot find libncurses.so.5
  | sysroots/x86_64-linux/usr/libexec/armv5te-oe-linux-gnueabi/gcc/arm-oe-linux-gnueabi/4.8.1/ld: warning: skipping incompatible sysroots/x86_64-linux/usr/lib/libtinfo.so while searching for tinfo
  | sysroots/x86_64-linux/usr/libexec/armv5te-oe-linux-gnueabi/gcc/arm-oe-linux-gnueabi/4.8.1/ld: error: cannot find -ltinfo
  | uhd/1_3.5.3-r3.0/git/host/examples/rx_ascii_art_dft.cpp:149: error: undefined reference to 'initscr'

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>