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

Using a fixed 3s polling timeout for all commands with R1B responses is a
bit problematic.

For some commands it means waiting longer than needed for the polling to be
aborted, which may not a big issue, but still. For other commands, like for
an erase (CMD38), may require longer timeouts than 3s. 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: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Cc: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20200414161413.3036-19-ulf.hansson@linaro.org