Fixed syntax error in function init_e300_core() of mpc83xx/start.S if

Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Heiko Schocher <hs@denx.de>

cpu/mpc83xx/start.S

@@ -462,7 +462,7 @@ init_e300_core: /* time t 10 */
 
 	li	r4, 0x556C
 	sth	r4, SWSRR@l(r3)
-	li	r4, 0xAA39
+	li	r4, -0x55C7
 	sth	r4, SWSRR@l(r3)
 #else
 	/* Disable Wathcdog  */