staging: mt7621-pci: remove bus ranges related code

Bus ranges are now discovered by default. Hence remove
its related code from the driver.

Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Link: https://lore.kernel.org/r/20201123093637.8300-2-sergio.paracuellos@gmail.com


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