mmc: core: Retry instead of ignore at CRC errors when polling for busy

After a CMD6 command has been sent, the __mmc_switch() function might be
advised to poll the card for busy by using CMD13 and also by ignoring CRC
errors.

In the case of ignoring CRC errors, the mmc core tells the mmc host to also
ignore these errors via masking the MMC_RSP_CRC response flag. This seems
wrong, as it leads to that the mmc host could propagate an unreliable
response, instead of a proper error code.

What we really want, is not to ignore CRC errors but instead retry the
polling attempt. So, let's change this by treating a CRC error as the card
is still being busy and thus continue to run the polling loop.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Tested-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>