staging: rtl8723bs: remove sd_f0_read8()

The sd_f0_read8() function, which is used by the sdio_f0_read8()
function, are not used anywhere in the driver and both can be
safely removed.

Signed-off-by: Bryan Brattlof <hello@bryanbrattlof.com>
Link: https://lore.kernel.org/r/20210524195144.1943280-1-hello@bryanbrattlof.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>