mmc: sh-mmcif: properly handle MMC_WRITE_MULTIPLE_BLOCK completion IRQ

Upon completion of a MMC_WRITE_MULTIPLE_BLOCK command MMCIF issues an IRQ
with the DTRANE bit set and often with one or several of CMD12 bits set.
If those interrupts are not acknowledged, an additional interrupt can be
produced and will be delivered later, possibly, when the transaction has
already been completed. To prevent this from happening, CMD12 completion
interrupt sources have to be cleared too upon reception of an DTRANE IRQ.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Tested-by: Tetsuyuki Kobayashi <koba@kmckk.co.jp>
Signed-off-by: Chris Ball <cjb@laptop.org>