staging: mt7621-mmc: Remove redundant host->mmc->f_max write

This is set once during initialization and never changed.  Don't bother
setting it again in the interrupt handler.

Signed-off-by: George Hilliard <thirtythreeforty@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>