mmc: core: Cleanup mmc_sd_num_wr_blocks() function

Use mmc_app_cmd() to avoid open-coding in mmc_sd_num_wr_blocks().

Signed-off-by: Victor Shih <victor.shih@genesyslogic.com.tw>
Link: https://lore.kernel.org/r/20230811101404.4463-1-victorshihgli@gmail.com


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