mmc: owl-mmc: Respect the cmd->busy_timeout from the mmc core

For commands that doesn't involve to prepare a data transfer, owl-mmc is
using a fixed 30s response timeout. This is a bit problematic.

For some commands it means waiting longer than needed for the completion to
expire, which may not a big issue, but still. For other commands, like for
an erase (CMD38) that uses a R1B response, may require longer timeouts than
30s. In these cases, we may end up treating the command as it failed, while
it just needed some more time to complete successfully.

Fix the problem by respecting the cmd->busy_timeout, which is provided by
the mmc core.

Cc: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20200414161413.3036-8-ulf.hansson@linaro.org