44x_spd_ddr.c: Fix GCC 4.6 build warnings

Fix:
44x_spd_ddr.c: In function 'program_cfg0':
44x_spd_ddr.c:384:16: warning: variable 'dimm_64bit' set but not used [-Wunused-but-set-variable]
44x_spd_ddr.c:383:16: warning: variable 'dimm_32bit' set but not used [-Wunused-but-set-variable]

Signed-off-by: Stefan Roese <sr@denx.de>