MIPS: dma-default: Defend against NULL dev in massage_gfp_flags

This patch ensures that the dev parameter is checked for NULL before it
is dereferenced in massage_gfp_flags. If dev is NULL, then fall back
setting the GFP flag requested and available.
Signed-off-by: NMatt Redfearn <matt.redfearn@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/11919/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

arch/mips/mm/dma-default.c

@@ -88,19 +88,20 @@ static gfp_t massage_gfp_flags(const struct device *dev, gfp_t gfp)
 	else
 #endif
 #if defined(CONFIG_ZONE_DMA32) && defined(CONFIG_ZONE_DMA)
-	     if (dev->coherent_dma_mask < DMA_BIT_MASK(32))
+	     if (dev == NULL || dev->coherent_dma_mask < DMA_BIT_MASK(32))
 			dma_flag = __GFP_DMA;
 	else if (dev->coherent_dma_mask < DMA_BIT_MASK(64))
 			dma_flag = __GFP_DMA32;
 	else
 #endif
 #if defined(CONFIG_ZONE_DMA32) && !defined(CONFIG_ZONE_DMA)
-	     if (dev->coherent_dma_mask < DMA_BIT_MASK(64))
+	     if (dev == NULL || dev->coherent_dma_mask < DMA_BIT_MASK(64))
 		dma_flag = __GFP_DMA32;
 	else
 #endif
 #if defined(CONFIG_ZONE_DMA) && !defined(CONFIG_ZONE_DMA32)
-	     if (dev->coherent_dma_mask < DMA_BIT_MASK(sizeof(phys_addr_t) * 8))
+	     if (dev == NULL ||
+		 dev->coherent_dma_mask < DMA_BIT_MASK(sizeof(phys_addr_t) * 8))
 		dma_flag = __GFP_DMA;
 	else
 #endif