If devm_pinctrl_get() fails then it leads to an error pointer
dereference. Add a check to prevent that.
Fixes: 99ad32a4ca3a ("mt76: mt7915: add support for MT7986") Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com> Signed-off-by: Felix Fietkau <nbd@nbd.name>