dmaengine: ioatdma: remove unused function missed during dma_v2 removal

Commit 7f832645 ("dmaengine: ioatdma: remove ioatdma v2 registration")
missed to remove dca2_tag_map_valid() during its removal. Hence, since
then, dca2_tag_map_valid() is unused and make CC=clang W=1 warns:

  drivers/dma/ioat/dca.c:44:19:
    warning: unused function 'dca2_tag_map_valid' [-Wunused-function]

So, remove this unused function and get rid of a -Wused-function warning.
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Link: https://lore.kernel.org/r/20201113081248.26416-1-lukas.bulwahn@gmail.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/ioat/dca.c

@@ -40,16 +40,6 @@
 #define DCA2_TAG_MAP_BYTE3 0x82
 #define DCA2_TAG_MAP_BYTE4 0x82
 
-/* verify if tag map matches expected values */
-static inline int dca2_tag_map_valid(u8 *tag_map)
-{
-	return ((tag_map[0] == DCA2_TAG_MAP_BYTE0) &&
-		(tag_map[1] == DCA2_TAG_MAP_BYTE1) &&
-		(tag_map[2] == DCA2_TAG_MAP_BYTE2) &&
-		(tag_map[3] == DCA2_TAG_MAP_BYTE3) &&
-		(tag_map[4] == DCA2_TAG_MAP_BYTE4));
-}
-
 /*
  * "Legacy" DCA systems do not implement the DCA register set in the
  * I/OAT device.  Software needs direct support for their tag mappings.