drm: mxsfb: Use dev_err_probe() helper

Use the dev_err_probe() helper, instead of open-coding the same
operation. This also adds a nice hint in
/sys/kernel/debug/devices_deferred.

Reviewed-by: Marek Vasut <marex@denx.de>
Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Signed-off-by: Marek Vasut <marex@denx.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20220202081755.145716-2-alexander.stein@ew.tq-group.com