staging: mt7621-pci: remove unnecessary check of device_type == pci

PCI host drivers have already matched on compatible strings, so checking
device_type is redundant. Also, device_type is considered deprecated for
FDT though we've still been requiring it for PCI hosts as it is useful
for finding PCI buses.

Cc: devel@driverdev.osuosl.org
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>