drm: fix a kernel-doc typo

Fix a build warning from 'make htmldocs' by correcting the lock name
in the kernel-doc comment.

include/drm/drm_file.h:369: warning: Function parameter or member 'master_lookup_lock' not described in 'drm_file'

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Reviewed-by: Simon Ser <contact@emersion.fr>
Signed-off-by: Simon Ser <contact@emersion.fr>
Link: https://patchwork.freedesktop.org/patch/msgid/20220403231040.18540-1-rdunlap@infradead.org