mmc_spi: Recover from CRC errors for r/w operation over SPI.

The SPI bus is not reliable for large data transfers on all platforms.
The current mmc_spi driver fails SD read/write commands immediately if
occasional CRC errors are reported by the SD device.  This patch makes
the operation recover from CRC errors by repeating the last SD command.
The retry count is set to 5 to ensure the driver passes stress tests.

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Chris Ball <cjb@laptop.org>