staging: mt7621-pinctrl: use tabs instead of spaces in some indentations

Kernel coding style use tabs for indent code instead of spaces.
Fix some places where spaces were being used silencing also
checkpatch script complains.

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