drm/fb: fix kernel-doc in drm_framebuffer.h

Fix following warnings:
drm_framebuffer.h:342: warning: Function parameter or member 'block_width' not described in 'drm_afbc_framebuffer'
drm_framebuffer.h:342: warning: Function parameter or member 'block_height' not described in 'drm_afbc_framebuffer'

Trivial spelling mistakes.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Andrzej Pietrasiewicz <andrzej.p@collabora.com>
Fixes: 55f7f727 ("drm/core: Add drm_afbc_framebuffer and a corresponding helper")
Cc: Andrzej Pietrasiewicz <andrzej.p@collabora.com>
Cc: Emil Velikov <emil.velikov@collabora.com>
Cc: James Qian Wang <james.qian.wang@arm.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20200328132025.19910-3-sam@ravnborg.org

include/drm/drm_framebuffer.h

@@ -308,11 +308,11 @@ struct drm_afbc_framebuffer {
 	 */
 	struct drm_framebuffer base;
 	/**
-	 * @block_widht: width of a single afbc block
+	 * @block_width: width of a single afbc block
 	 */
 	u32 block_width;
 	/**
-	 * @block_widht: height of a single afbc block
+	 * @block_height: height of a single afbc block
 	 */
 	u32 block_height;
 	/**