cam5200_niosflash: fix build warnings

Fix warnings:

cam5200_flash.c: In function 'write_word_32':
cam5200_flash.c:443: warning: dereferencing type-punned pointer will break strict-aliasing rules
cam5200_flash.c: In function 'write_word_16':
cam5200_flash.c:684: warning: dereferencing type-punned pointer will break strict-aliasing rules

Signed-off-by: Wolfgang Denk <wd@denx.de>
Acked-by: Stefan Roese <sr@denx.de>