mmc: dw_mmc: fix error handling in PIO mode

Data transfer will be continued until all the bytes are transmitted,
even if data crc error occurs during a multiple-block data transfer.
This means RXDR/TXDR interrupts will occurs until data transfer is
terminated. Early setting of host->sg to NULL prevents going into
xxx_data_pio functions, hence permanent unhandled RXDR/TXDR interrupts
occurs. And checking error interrupt status in the xxx_data_pio functions
is no need because dw_mci_interrupt does do the same. This patch also
removes it.

Signed-off-by: Seungwon Jeon <tgih.jun@samsung.com>
Acked-by: Jaehoon Chung <jh80.chung@samsung.com>
Acked-by: Will Newton <will.newton@imgtec.com>
Signed-off-by: Chris Ball <cjb@laptop.org>