drm: fix trivial coding errors

Correct function storage class, and correct assignment type.
Signed-off-by: NDaniel J Blueman <daniel.blueman@gmail.com>
Reviewed-by: NAlex Deucher <alexdeucher@gmail.com>
Signed-off-by: NDave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_buffer.c

@@ -98,7 +98,7 @@ EXPORT_SYMBOL(drm_buffer_alloc);
  *   user_data: A pointer the data that is copied to the buffer.
  *   size: The Number of bytes to copy.
  */
-extern int drm_buffer_copy_from_user(struct drm_buffer *buf,
+int drm_buffer_copy_from_user(struct drm_buffer *buf,
 			      void __user *user_data, int size)
 {
 	int nr_pages = size / PAGE_SIZE + 1;
@@ -163,7 +163,7 @@ void *drm_buffer_read_object(struct drm_buffer *buf,
 {
 	int idx = drm_buffer_index(buf);
 	int page = drm_buffer_page(buf);
-	void *obj = 0;
+	void *obj = NULL;
 
 	if (idx + objsize <= PAGE_SIZE) {
 		obj = &buf->data[page][idx];