drm: Spelling s/sempahore/semaphore/

Fix misspellings of "semaphore".

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/8b0542c12a2427f34a792c41ac2d2a2922874bfa.1689600102.git.geert+renesas@glider.be