drm/msm: Remove fb from struct msm_fbdev

Fbdev's struct fb_helper stores a pointer to the framebuffer. Remove
struct msm_fbdev.fb, which contains thre same value. No functional
changes.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/530552/
Link: https://lore.kernel.org/r/20230403124538.8497-4-tzimmermann@suse.de


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>