board/esd/cpci750/ide.c: fix compile warning

Fix warning: ide.c:54: warning: dereferencing type-punned pointer will
break strict-aliasing rules

Signed-off-by: Wolfgang Denk <wd@denx.de>
Cc: Matthias Fuchs <matthias.fuchs@esd-electronics.com>
Cc: Stefan Roese <sr@denx.de>
Acked-by: Stefan Roese <sr@denx.de>