Fix compiler warnings for EVB64260, P3G4 and ZUMA

Fix following warnings:

$ ./MAKEALL EVB64260 P3G4 ZUMA
Configuring for EVB64260 board...
mpsc.c: In function 'mpsc_putchar_early':
mpsc.c:121: warning: dereferencing type-punned pointer will break strict-aliasing rules
mpsc.c:127: warning: dereferencing type-punned pointer will break strict-aliasing rules
...

Signed-off-by: Anatolij Gustschin <agust@denx.de>

board/evb64260/mpsc.c

@@ -88,7 +88,7 @@ static void galsdma_enable_rx(void);
 
 
 /* GT64240A errata: cant read MPSC/BRG registers... so make mirrors in ram for read/modify write */
-#define MIRROR_HACK ((struct _tag_mirror_hack *)&(gd->mirror_hack))
+#define MIRROR_HACK ((struct _tag_mirror_hack *)&(gd->mirror_hack[0]))
 
 #define GT_REG_WRITE_MIRROR_G(a,d) {MIRROR_HACK->a ## _M = d; GT_REG_WRITE(a,d);}
 #define GTREGREAD_MIRROR_G(a) (MIRROR_HACK->a ## _M)