GCC4.6: Squash warning in cmd_mem.c

GCC4.6: Squash warning in cmd_mem.c

cmd_mem.c: In function ‘do_mem_loop’:
cmd_mem.c:474:25: warning: variable ‘junk’ set but not used
[-Wunused-but-set-variable]

The assigned variable can be removed because the pointers are volatile so
accesses to their addresses are always generated.

Signed-off-by: Marek Vasut <marek.vasut@gmail.com>
[sw0312.kim: cherry-pick from mainline commit f3b3c3df189f to fix build warning]
Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Change-Id: I20e93f08dc0e7fbc73fbfdf213781948f9737eb7