powerpc: mpc85xx: use CONFIG_VAL() for SYS_MONITOR_BASE in start.s

Use CONFIG_VAL() for SYS_MONITOR_BASE in start.S so that correct value
is used for SPL.

Signed-off-by: Marek Mojík <marek.mojik@nic.cz>
Reviewed-by: Marek Behún <kabel@kernel.org>
diff --git a/arch/powerpc/cpu/mpc85xx/start.S b/arch/powerpc/cpu/mpc85xx/start.S
index b737d5d..3e24a90 100644
--- a/arch/powerpc/cpu/mpc85xx/start.S
+++ b/arch/powerpc/cpu/mpc85xx/start.S
@@ -116,7 +116,7 @@
 	.long (CONFIG_FSL_PREPBL_ESDHC_BOOT_SECTOR_START + CONFIG_FSL_PREPBL_ESDHC_BOOT_SECTOR_DATA) * 512
 
 	.org 0x58 /* Target address in the system's local memory address space */
-	.long CONFIG_SYS_MONITOR_BASE
+	.long CONFIG_VAL(SYS_MONITOR_BASE)
 
 	.org 0x60 /* Execution starting address */
 	.long _start