staging: mt7621-gpio: set irq chip name only once

There is only one irq chip so set its name only once
in driver probe function.

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