staging: mt7621-pci: move some code into 'mt7621_pcie_init_ports'

Some clocks bits related code is in driver probe function and can
perfectly be moved into 'mt7621_pcie_init_ports' function which is
a more accurate place for it.

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