drm: fix drm_fb_xrgb8888_to_rgb888_dstclip()

Oops, the __iomem annotation was added to the header file only.
Add it to the implementation (and documentation) too.

Fixes: 5c5373b5 ("drm: switch drm_fb_xrgb8888_to_rgb888_dstclip to accept __iomem dst")
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>
Reviewed-by: NNoralf Trønnes <noralf@tronnes.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20190411044932.13247-1-kraxel@redhat.com

drivers/gpu/drm/drm_format_helper.c

@@ -230,7 +230,7 @@ static void drm_fb_xrgb8888_to_rgb888_line(u8 *dbuf, u32 *sbuf,
 
 /**
  * drm_fb_xrgb8888_to_rgb888_dstclip - Convert XRGB8888 to RGB888 clip buffer
- * @dst: RGB565 destination buffer
+ * @dst: RGB565 destination buffer (iomem)
  * @dst_pitch: destination buffer pitch
  * @vaddr: XRGB8888 source buffer
  * @fb: DRM framebuffer
@@ -241,9 +241,9 @@ static void drm_fb_xrgb8888_to_rgb888_line(u8 *dbuf, u32 *sbuf,
  * support XRGB8888.
  *
  * This function applies clipping on dst, i.e. the destination is a
- * full framebuffer but only the clip rect content is copied over.
+ * full (iomem) framebuffer but only the clip rect content is copied over.
  */
-void drm_fb_xrgb8888_to_rgb888_dstclip(void *dst, unsigned int dst_pitch,
+void drm_fb_xrgb8888_to_rgb888_dstclip(void __iomem *dst, unsigned int dst_pitch,
 				       void *vaddr, struct drm_framebuffer *fb,
 				       struct drm_rect *clip)
 {