mmc: debugfs: convert permissions to octal

Convert the existing symbolic permissions to the octal presentation as
this is the preferred representation for debugfs permissions.

Signed-off-by: Rouven Czerwinski <r.czerwinski@pengutronix.de>
Link: https://lore.kernel.org/r/20240326094215.212930-1-r.czerwinski@pengutronix.de


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