staging: mt7621-pinctrl: Use correct pointer type argument for sizeof

Fix the following coccicheck warning:

drivers/staging/mt7621-pinctrl/pinctrl-rt2880.c:223:14-36: WARNING: Use
correct pointer type argument for sizeof

Signed-off-by: Jason Yan <yanaijie@huawei.com>
Link: https://lore.kernel.org/r/20200420133416.3087-1-yanaijie@huawei.com


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