iommu/exynos: Replace non-existing big-endian Kconfig option

Wrong Kconfig option was used when adding warning for untested
big-endian capabilities. There is no CONFIG_BIG_ENDIAN option.
Signed-off-by: NKrzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: NJoerg Roedel <jroedel@suse.de>

drivers/iommu/exynos-iommu.c

@@ -54,7 +54,7 @@ typedef u32 sysmmu_pte_t;
 #define lv2ent_small(pent) ((*(pent) & 2) == 2)
 #define lv2ent_large(pent) ((*(pent) & 3) == 1)
 
-#ifdef CONFIG_BIG_ENDIAN
+#ifdef CONFIG_CPU_BIG_ENDIAN
 #warning "revisit driver if we can enable big-endian ptes"
 #endif