staging: mt7621-pci: use {readl|writel}_relaxed instead of readl/writel

The driver does not perform DMA, so it's safe to use the relaxed version
for both readl and writel operations.

Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Link: https://lore.kernel.org/r/20210607120153.24989-4-sergio.paracuellos@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>