drm/omap: gem: Fix misnamed and missing parameter descriptions

Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/omapdrm/omap_gem.c:593: warning: Function parameter or member 'file' not described in 'omap_gem_dumb_create'
 drivers/gpu/drm/omapdrm/omap_gem.c:593: warning: Excess function parameter 'drm_file' description in 'omap_gem_dumb_create'
 drivers/gpu/drm/omapdrm/omap_gem.c:619: warning: Function parameter or member 'offset' not described in 'omap_gem_dumb_map_offset'

Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: Rob Clark <rob.clark@linaro.org>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201106214949.2042120-9-lee.jones@linaro.org

drivers/gpu/drm/omapdrm/omap_gem.c

@@ -580,7 +580,7 @@ int omap_gem_mmap_obj(struct drm_gem_object *obj,
 
 /**
  * omap_gem_dumb_create	-	create a dumb buffer
- * @drm_file: our client file
+ * @file: our client file
  * @dev: our device
  * @args: the requested arguments copied from userspace
  *
@@ -610,6 +610,7 @@ int omap_gem_dumb_create(struct drm_file *file, struct drm_device *dev,
  * @file: our drm client file
  * @dev: drm device
  * @handle: GEM handle to the object (from dumb_create)
+ * @offset: memory map offset placeholder
  *
  * Do the necessary setup to allow the mapping of the frame buffer
  * into user memory. We don't have to do much here at the moment.