mtd: brcmnand: Fix misuse of IS_ENABLED

While IS_ENABLED() is perfectly fine for CONFIG_* symbols, it is not
for other symbols such as __BIG_ENDIAN that is provided directly by
the compiler.

Switch to use CONFIG_CPU_BIG_ENDIAN instead of __BIG_ENDIAN.

Fixes: 27c5b17cd1 ("mtd: nand: add NAND driver "library" for Broadcom STB NAND controller")
Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

drivers/mtd/nand/brcmnand/brcmnand.h

@@ -50,7 +50,7 @@ static inline u32 brcmnand_readl(void __iomem *addr)
 	 * Other architectures (e.g., ARM) either do not support big endian, or
 	 * else leave I/O in little endian mode.
 	 */
-	if (IS_ENABLED(CONFIG_MIPS) && IS_ENABLED(__BIG_ENDIAN))
+	if (IS_ENABLED(CONFIG_MIPS) && IS_ENABLED(CONFIG_CPU_BIG_ENDIAN))
 		return __raw_readl(addr);
 	else
 		return readl_relaxed(addr);
@@ -59,7 +59,7 @@ static inline u32 brcmnand_readl(void __iomem *addr)
 static inline void brcmnand_writel(u32 val, void __iomem *addr)
 {
 	/* See brcmnand_readl() comments */
-	if (IS_ENABLED(CONFIG_MIPS) && IS_ENABLED(__BIG_ENDIAN))
+	if (IS_ENABLED(CONFIG_MIPS) && IS_ENABLED(CONFIG_CPU_BIG_ENDIAN))
 		__raw_writel(val, addr);
 	else
 		writel_relaxed(val, addr);