MIPS: Octeon: Avoid empty-body warning

gcc-6 reports a harmless build warning:

arch/mips/cavium-octeon/dma-octeon.c: In function 'octeon_dma_alloc_coherent':
arch/mips/cavium-octeon/dma-octeon.c:179:3: error: suggest braces around empty body in an 'else' statement [-Werror=empty-body]

We can fix this by rearranging the code slightly using the
IS_ENABLED() macro.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Hans-Christian Noren Egtvedt <egtvedt@samfundet.no>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/15048
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/cavium-octeon/dma-octeon.c

@@ -164,19 +164,14 @@ static void *octeon_dma_alloc_coherent(struct device *dev, size_t size,
 	/* ignore region specifiers */
 	gfp &= ~(__GFP_DMA | __GFP_DMA32 | __GFP_HIGHMEM);
 
-#ifdef CONFIG_ZONE_DMA
-	if (dev == NULL)
+	if (IS_ENABLED(CONFIG_ZONE_DMA) && dev == NULL)
 		gfp |= __GFP_DMA;
-	else if (dev->coherent_dma_mask <= DMA_BIT_MASK(24))
+	else if (IS_ENABLED(CONFIG_ZONE_DMA) &&
+		 dev->coherent_dma_mask <= DMA_BIT_MASK(24))
 		gfp |= __GFP_DMA;
-	else
-#endif
-#ifdef CONFIG_ZONE_DMA32
-	     if (dev->coherent_dma_mask <= DMA_BIT_MASK(32))
+	else if (IS_ENABLED(CONFIG_ZONE_DMA32) &&
+		 dev->coherent_dma_mask <= DMA_BIT_MASK(32))
 		gfp |= __GFP_DMA32;
-	else
-#endif
-		;
 
 	/* Don't invoke OOM killer */
 	gfp |= __GFP_NORETRY;