mmc: core: Remove unnecessary error checks and change return type

The error checks in mmc_blk_add_debugfs() and mmc_blk_remove_debugfs()
are extraneous. Therefore, this patch removes all error checks from
both functions.
Additionally, mmc_blk_add_debugfs() has been changed to return void
instead of an integer value that was never used. This simplifies the
function and improves its clarity.

Signed-off-by: Yeqi Fu <asuk4.q@gmail.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/20230518101216.369970-1-asuk4.q@gmail.com


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