mmc: sdhci-of-at91: replace while loop with read_poll_timeout

Replace while loop with read_poll_timeout().

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20210924082851.2132068-3-claudiu.beznea@microchip.com


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