PCI: mt7621: Add sentinel to quirks table

Current driver is missing a sentinel in the struct soc_device_attribute
array, which causes an oops when assessed by the
soc_device_match(mt7621_pcie_quirks_match) call.

This was only exposed once the CONFIG_SOC_MT7621 mt7621 soc_dev_attr
was fixed to register the SOC as a device, in:

commit 7c18b64b ("mips: ralink: mt7621: do not use kzalloc too early")

Fix it by adding the required sentinel.

Link: https://lore.kernel.org/lkml/26ebbed1-0fe9-4af9-8466-65f841d0b382@app.fastmail.com
Link: https://lore.kernel.org/r/20221205204645.301301-1-git@johnthomson.fastmail.com.au


Fixes: b483b4e4 ("staging: mt7621-pci: add quirks for 'E2' revision using 'soc_device_attribute'")
Signed-off-by: John Thomson <git@johnthomson.fastmail.com.au>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Acked-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>