microblaze: Remove device_to_mask

Completely unused function - remove it.
Signed-off-by: Michal Simek <michal.simek@xilinx.com>

arch/microblaze/include/asm/dma-mapping.h

@@ -35,14 +35,6 @@
 #define __dma_alloc_coherent(dev, gfp, size, handle)	NULL
 #define __dma_free_coherent(size, addr)		((void)0)
 
-static inline unsigned long device_to_mask(struct device *dev)
-{
-	if (dev->dma_mask && *dev->dma_mask)
-		return *dev->dma_mask;
-	/* Assume devices without mask can take 32 bit addresses */
-	return 0xfffffffful;
-}
-
 /*
  * Available generic sets of operations
  */