MIPS: Loongson64: Fix empty-body warning in dma_alloc

A new gcc warning shows up for this old code with gcc-6:

arch/mips/loongson64/common/dma-swiotlb.c: In function 'loongson_dma_alloc_coherent':
arch/mips/loongson64/common/dma-swiotlb.c:35:2: error: suggest braces around empty body in an 'else' statement [-Werror=empty-body]

The code can be easily restructured to look more readable
and avoid the warning at the same time.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/15047/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/loongson64/common/dma-swiotlb.c

@@ -17,22 +17,14 @@ static void *loongson_dma_alloc_coherent(struct device *dev, size_t size,
 	/* ignore region specifiers */
 	gfp &= ~(__GFP_DMA | __GFP_DMA32 | __GFP_HIGHMEM);
 
-#ifdef CONFIG_ISA
-	if (dev == NULL)
+	if ((IS_ENABLED(CONFIG_ISA) && dev == NULL) ||
+	    (IS_ENABLED(CONFIG_ZONE_DMA) &&
+	     dev->coherent_dma_mask < DMA_BIT_MASK(32)))
 		gfp |= __GFP_DMA;
-	else
-#endif
-#ifdef CONFIG_ZONE_DMA
-	if (dev->coherent_dma_mask < DMA_BIT_MASK(32))
-		gfp |= __GFP_DMA;
-	else
-#endif
-#ifdef CONFIG_ZONE_DMA32
-	if (dev->coherent_dma_mask < DMA_BIT_MASK(40))
+	else if (IS_ENABLED(CONFIG_ZONE_DMA32) &&
+		 dev->coherent_dma_mask < DMA_BIT_MASK(40))
 		gfp |= __GFP_DMA32;
-	else
-#endif
-	;
+
 	gfp |= __GFP_NORETRY;
 
 	ret = swiotlb_alloc_coherent(dev, size, dma_handle, gfp);