drm/ttm: fix function prototype to match implementation

Fix function prototype to match its actual usage and implementation.

drivers/gpu/drm/ttm/ttm_bo_util.c:341:10: error: symbol 'ttm_io_prot' redeclared with different type (originally declared at include/drm/ttm/ttm_bo_driver.h:911) - incompatible argument 1 (different signedness)
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc:	David Airlie <airlied@linux.ie>
Signed-off-by: Dave Airlie <airlied@redhat.com>

include/drm/ttm/ttm_bo_driver.h

@@ -908,7 +908,7 @@ extern int ttm_bo_move_accel_cleanup(struct ttm_buffer_object *bo,
  * Utility function that returns the pgprot_t that should be used for
  * setting up a PTE with the caching model indicated by @c_state.
  */
-extern pgprot_t ttm_io_prot(enum ttm_caching_state c_state, pgprot_t tmp);
+extern pgprot_t ttm_io_prot(uint32_t caching_flags, pgprot_t tmp);
 
 #if (defined(CONFIG_AGP) || (defined(CONFIG_AGP_MODULE) && defined(MODULE)))
 #define TTM_HAS_AGP