drm/vmwgfx: fix a warning message

The WARN_ON() macro only takes a condition argument, it doesn't take
a message.  I have converted this to WARN() instead.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Sinclair Yeh <syeh@vmware.com>
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_fifo.c b/drivers/gpu/drm/vmwgfx/vmwgfx_fifo.c
index a8baf5f..b6a0806 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_fifo.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_fifo.c
@@ -390,7 +390,7 @@
 	else if (ctx_id == SVGA3D_INVALID_ID)
 		ret = vmw_local_fifo_reserve(dev_priv, bytes);
 	else {
-		WARN_ON("Command buffer has not been allocated.\n");
+		WARN(1, "Command buffer has not been allocated.\n");
 		ret = NULL;
 	}
 	if (IS_ERR_OR_NULL(ret)) {