drm/gma500/framebuffer: Fix some possible doc-rot issues

drm/gma500/framebuffer: Fix some possible doc-rot issues

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

 drivers/gpu/drm/gma500/framebuffer.c:171: warning: Function parameter or member 'obj' not described in 'psb_framebuffer_init'
 drivers/gpu/drm/gma500/framebuffer.c:171: warning: Excess function parameter 'gt' description in 'psb_framebuffer_init'
 drivers/gpu/drm/gma500/framebuffer.c:212: warning: Function parameter or member 'obj' not described in 'psb_framebuffer_create'
 drivers/gpu/drm/gma500/framebuffer.c:212: warning: Excess function parameter 'gt' description in 'psb_framebuffer_create'
 drivers/gpu/drm/gma500/framebuffer.c:262: warning: Function parameter or member 'fb_helper' not described in 'psbfb_create'
 drivers/gpu/drm/gma500/framebuffer.c:262: warning: Excess function parameter 'fbdev' description in 'psbfb_create'

Cc: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210115181313.3431493-15-lee.jones@linaro.org