phy: phy-brcm-usb: improve getting OF matching data

1. Use of_device_get_match_data() helper to simplify the code
2. Check for NULL as a good practice

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20201216143305.12179-1-zajec5@gmail.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>