mmc: sdhci-brcmstb: Fix mmc timeout errors on S5 suspend

mmc: sdhci-brcmstb: Fix mmc timeout errors on S5 suspend

Commit e7b5d63a82fe ("mmc: sdhci-brcmstb: Add shutdown callback")
that added a shutdown callback to the diver, is causing "mmc timeout"
errors on S5 suspend. The problem was that the "remove" was queuing
additional MMC commands after the "shutdown" and these caused
timeouts as the MMC queues were cleaned up for "remove". The
shutdown callback will be changed to calling sdhci-pltfm_suspend
which should get better power savings because the clocks will be
shutdown.

Fixes: e7b5d63a82fe ("mmc: sdhci-brcmstb: Add shutdown callback")
Signed-off-by: Al Cooper <alcooperx@gmail.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20210107221509.6597-1-alcooperx@gmail.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>