mmc: mtk-sd: Use readl_poll_timeout instead of open-coded polling

Replace all instances of open-coded while loops for polling registers
with calls to readl_poll_timeout() and, while at it, also fix some
possible infinite loop instances.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20211216125748.179602-1-angelogioacchino.delregno@collabora.com


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>