ppc4xx: Fix small 405EZ OCM initilization bug in start.S

As pointed out by Bruce Adler <bruce.adler@acm.org> this patch
fixes a small bug in the 405EZ OCM initialization. Thanks for
spotting.
Signed-off-by: NStefan Roese <sr@denx.de>

cpu/ppc4xx/start.S

@@ -783,7 +783,7 @@ _start:
 	mtdcr	ocmdscr2, r3            /* Set Data Side */
 	mtdcr	ocmiscr2, r3            /* Set Instruction Side */
 	addis	r3,0,0x0800             /* OCM Data Parity Disable - 1 Wait State */
-	mtdcr	ocmdsisdpc,r4
+	mtdcr	ocmdsisdpc,r3
 
 	isync
 #else /* CONFIG_405EZ */