mmc: sdhci-xenon: 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: Hu Ziji <huziji@marvell.com>
Signed-off-by: Binbin Zhou <zhoubinbin@loongson.cn>
Link: https://lore.kernel.org/r/e7c52155f04fc270400985b70514800c23fd5565.1749127796.git.zhoubinbin@loongson.cn


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