board/ep82xxm/ep82xxm.c: Fix GCC 4.6 build warning

Fix:
ep82xxm.c: In function 'initdram':
ep82xxm.c:233:16: warning: variable 'ramtmp' set but not used
[-Wunused-but-set-variable]

Signed-off-by: Wolfgang Denk <wd@denx.de>