drm: Fix htmldocs warnings in drm_fourcc.c

drm: Fix htmldocs warnings in drm_fourcc.c

Add a description for dev and remove the excess one for native. Fixes
the following warnings:

../drivers/gpu/drm/drm_fourcc.c:112: warning: Function parameter or member 'dev' not described in 'drm_driver_legacy_fb_format'
../drivers/gpu/drm/drm_fourcc.c:112: warning: Excess function parameter 'native' description in 'drm_driver_legacy_fb_format'

Fixes: 059b5eb5d955 ("drm: move native byte order quirk to new drm_driver_legacy_fb_format function")
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20181107205546.216088-1-sean@poorly.run