MAINTAINERS: repair reference in DRM DRIVER FOR SIMPLE FRAMEBUFFERS

Commit 11e8f5fd ("drm: Add simpledrm driver") adds the file
./drivers/gpu/drm/tiny/simpledrm.c, but refers to the file
./drivers/gpu/drm/tiny/simplekms.c with the new MAINTAINERS section
DRM DRIVER FOR SIMPLE FRAMEBUFFERS.

Hence, ./scripts/get_maintainer.pl --self-test=patterns complains:

  warning: no file matches    F:    drivers/gpu/drm/tiny/simplekms.c

Repair the file entry by referring to the right location.
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20210517101648.29906-1-lukas.bulwahn@gmail.com

MAINTAINERS

@@ -5875,7 +5875,7 @@ M:	Thomas Zimmermann <tzimmermann@suse.de>
 L:	dri-devel@lists.freedesktop.org
 S:	Maintained
 T:	git git://anongit.freedesktop.org/drm/drm-misc
-F:	drivers/gpu/drm/tiny/simplekms.c
+F:	drivers/gpu/drm/tiny/simpledrm.c
 
 DRM DRIVER FOR SIS VIDEO CARDS
 S:	Orphan / Obsolete