video: mxfsb: Fix endless -EPROBE_DEFER with empty disp_dev

video: mxfsb: Fix endless -EPROBE_DEFER with empty disp_dev

Since f7b48681ec68 ("MLK-16137 video: fbdev: add defer probe for mxs framebuffer")
the mxsfb_dispdrv_init function will return -EPROBE_DEFER on all
mxc_dispdrv_gethandle failures. That makes sense because all
mxc_dispdrv_entry are registered in their respective probe functions and
an absent entry should result in probing mxsfb later.

However in some cases an the disp_dev is empty and those configurations
now result in enless EPROBE_DEFER loops. Fix this by accepting empty
disp_dev at the start of mxsfb_dispdrv_init.

Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
Reviewed-by: Robert Chiras <robert.chiras@nxp.com>