board/sbc405/strataflash.c: Fix GCC 4.6 build warning

Fix:
strataflash.c: In function 'flash_write_cfiword':
strataflash.c:673:11: warning: variable 'ctladdr' set but not used
[-Wunused-but-set-variable]

Signed-off-by: Wolfgang Denk <wd@denx.de>
Acked-by: Marek Vasut <marek.vasut@gmail.com>