mmc: sdhci-of-k1: Drop the use of sdhci_pltfm_free()

mmc: sdhci-of-k1: 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: Yixun Lan <dlan@gentoo.org>
Cc: linux-riscv@lists.infradead.org
Cc: spacemit@lists.linux.dev
Reviewed-by: Yixun Lan <dlan@gentoo.org>
Signed-off-by: Binbin Zhou <zhoubinbin@loongson.cn>
Link: https://lore.kernel.org/r/e98c6383c82a0af2dce6d07645c9fecd53de8767.1749127796.git.zhoubinbin@loongson.cn
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>