OMAP4: avoid null pointer access in save_boot_params

When booting via spl the parameter layout is apparently different
and this leads to following bad pointers.

For now just work around the issue by checking pointers before
following them.

Signed-off-by: John Rigby <john.rigby@linaro.org>
diff --git a/arch/arm/cpu/armv7/omap-common/lowlevel_init.S b/arch/arm/cpu/armv7/omap-common/lowlevel_init.S
index 3581077..d5b2ed4 100644
--- a/arch/arm/cpu/armv7/omap-common/lowlevel_init.S
+++ b/arch/arm/cpu/armv7/omap-common/lowlevel_init.S
@@ -66,7 +66,13 @@
 	bgt	2f
 	/* Store the boot mode (raw/FAT) in omap_bootmode */
 	ldr	r2, [r0, #DEV_DESC_PTR_OFFSET]	@ get the device descriptor ptr
+	bic	r3, r2, #255
+	cmp	r3, #0
+	beq	1f
 	ldr	r2, [r2, #DEV_DATA_PTR_OFFSET]	@ get the pDeviceData ptr
+	bic	r3, r2, #255
+	cmp	r3, #0
+	beq	1f
 	ldr	r2, [r2, #BOOT_MODE_OFFSET]	@ get the boot mode
 	ldr	r3, =omap_bootmode
 	str	r2, [r3]