mmc: tmio: fix regression in TMIO_MMC_WRPROTECT_DISABLE handling

Commit b6147490

 ("mmc: tmio: split core functionality, DMA and
MFD glue") broke handling of the TMIO_MMC_WRPROTECT_DISABLE flag by
the tmio-mmc driver. This patch restores the original behaviour.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Cc: <stable@kernel.org>
Signed-off-by: Chris Ball <cjb@laptop.org>