staging: mt7621-pci: avoid using clk_* operations

There is no clock driver for ralink mips and clk_enable
are no-ops for this architecture. This has been also tested
without using clocks and seems to work so avoid to use them
in this driver.

Fixes: ad9c87e1: "staging: mt7621-pci: parse and init
port data from device tree"
Reported-by: NeilBrown <neil@brown.name>

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