mmc: litex_mmc: Use devm_mmc_alloc_host() helper

mmc: litex_mmc: Use devm_mmc_alloc_host() helper

Use new function devm_mmc_alloc_host() to simplify the code.

Cc: Karol Gugala <kgugala@antmicro.com>
Cc: Mateusz Holenko <mholenko@antmicro.com>
Cc: Gabriel Somlo <gsomlo@gmail.com>
Cc: Joel Stanley <joel@jms.id.au>
Reviewed-by: Huacai Chen <chenhuacai@loongson.cn>
Acked-by: Gabriel Somlo <gsomlo@gmail.com>
Signed-off-by: Binbin Zhou <zhoubinbin@loongson.cn>
Link: https://lore.kernel.org/r/8eea32bf0fb1ac95497355ccd5ea732ce619238c.1748933789.git.zhoubinbin@loongson.cn
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>