phy: ralink: mt7621-pci: add sentinel to quirks table

With mt7621 soc_dev_attr fixed to register the soc as a device,
kernel will experience an oops in soc_device_match_attr

This quirk test was introduced in the staging driver in
commit 9445ccb3 ("staging: mt7621-pci-phy: add quirks for 'E2'
revision using 'soc_device_attribute'"). The staging driver was removed,
and later re-added in commit d87da323 ("phy: ralink: Add PHY driver
for MT7621 PCIe PHY") for kernel 5.11

Link: https://lore.kernel.org/lkml/26ebbed1-0fe9-4af9-8466-65f841d0b382@app.fastmail.com
Fixes: d87da323

 ("phy: ralink: Add PHY driver for MT7621 PCIe PHY")
Signed-off-by: John Thomson <git@johnthomson.fastmail.com.au>
Acked-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Link: https://lore.kernel.org/r/20221104205242.3440388-2-git@johnthomson.fastmail.com.au
Signed-off-by: Vinod Koul <vkoul@kernel.org>