mmc: sdhci-of-at91: Drop the use of sdhci_pltfm_free()

mmc: sdhci-of-at91: Drop the use of sdhci_pltfm_free()

Since the devm_mmc_alloc_host() helper is already in use,
sdhci_pltfm_free() is no longer needed.

Cc: Aubin Constans <aubin.constans@microchip.com>
Cc: Eugen Hristev <eugen.hristev@linaro.org>
Cc: Nicolas Ferre <nicolas.ferre@microchip.com>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: Claudiu Beznea <claudiu.beznea@tuxon.dev>
Signed-off-by: Binbin Zhou <zhoubinbin@loongson.cn>
Acked-by: Aubin Constans <aubin.constans@microchip.com>
Link: https://lore.kernel.org/r/d64ed0f849277760d5b9ce04cfff1cd02ad43d19.1749127796.git.zhoubinbin@loongson.cn
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>