tftp-hpa: fix a build failure

AR is defined as "ar cq" in MCONFIG.in, then "cq" is no longer needed in
Makefile of common and libs subdir.
	#grep AR MCONFIG.in
	AR	= ar cq
	#

	#grep AR common/Makefile
	$(AR) $(LIB) $(OBJS)
	#
But MCONFIG maybe not able to be generated by MCONFIG.in, common/Makefile
allows this condition [Note the - before include]
	#grep MCONFIG common/Makefile
	-include ../MCONFIG
	#
then AR from building environment is used, but it not included the parameter
"cq", and lead to below error, so add the "cq" to AR to fix this issue.
	i586-wrs-linux-ar libcommon.a tftpsubs.
	i586-wrs-linux-ar: two different operation options specified

Signed-off-by: Roy Li <rongqing.li@windriver.com>
Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>