staging: mt7621-pci: enable interrupt when port is being enabled

Interrupt is being enabled in port initialization when the port phy
has not been initialized yet. Just enable the interrupt when the port
is being enabled which is a more accurate place for this.

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