staging: mt7621-pinctrl: replace 'unsigned' types with 'unsigned int'

This commit replaces all 'unsigned' type declarations along
the driver code in favour of the preferred one 'unsigned int'.
This also silence checkpatch script warnings about this issue.

Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>