synergy: add dependency on unzip-native

* otherwise may fail with:
  ERROR: synergy-1.7.3+1.7.4-rc8+AUTOINC+588fb4b805-r0 do_unpack_extra: Function failed: do_unpack_extra (log file is located at /home/jenkins/oe/world/shr-core/tmp-glibc/work/armv5te-oe-linux-gnueabi/synergy/1.7.3+1.7.4-rc8+AUTOINC+588fb4b805-r0/temp/log.do_unpack_extra.11874)
  ERROR: Logfile of failure stored in: /home/jenkins/oe/world/shr-core/tmp-glibc/work/armv5te-oe-linux-gnueabi/synergy/1.7.3+1.7.4-rc8+AUTOINC+588fb4b805-r0/temp/log.do_unpack_extra.11874
  Log data follows:
  | DEBUG: Executing shell function do_unpack_extra
  | /home/jenkins/oe/world/shr-core/tmp-glibc/work/armv5te-oe-linux-gnueabi/synergy/1.7.3+1.7.4-rc8+AUTOINC+588fb4b805-r0/temp/run.do_unpack_extra.11874: 105: /home/jenkins/oe/world/shr-core/tmp-glibc/work/armv5te-oe-linux-gnueabi/synergy/1.7.3+1.7.4-rc8+AUTOINC+588fb4b805-r0/temp/run.do_unpack_extra.11874: unzip: not found
  | WARNING: exit code 127 from a shell command.
  | ERROR: Function failed: do_unpack_extra (log file is located at /home/jenkins/oe/world/shr-core/tmp-glibc/work/armv5te-oe-linux-gnueabi/synergy/1.7.3+1.7.4-rc8+AUTOINC+588fb4b805-r0/temp/log.do_unpack_extra.11874)
  NOTE: recipe synergy-1.7.3+1.7.4-rc8+AUTOINC+588fb4b805-r0: task do_unpack_extra: Failed
  ERROR: Task 0 (/home/jenkins/oe/world/shr-core/meta-openembedded/meta-oe/recipes-support/synergy/synergy_git.bb, do_unpack_extra) failed with exit code '1'

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