wifi: mt76: mt7996: Check phy before init msta_link in mt7996_mac_sta_add_links()

wifi: mt76: mt7996: Check phy before init msta_link in mt7996_mac_sta_add_links()

In order to avoid a possible NULL pointer dereference in
mt7996_mac_sta_init_link routine, move the phy pointer check before
running mt7996_mac_sta_init_link() in mt7996_mac_sta_add_links routine.

Fixes: dd82a9e02c054 ("wifi: mt76: mt7996: Rely on mt7996_sta_link in sta_add/sta_remove callbacks")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://patch.msgid.link/20250830-mt7996_mac_sta_add_links-fix-v1-1-4219fb8755ee@kernel.org
Signed-off-by: Felix Fietkau <nbd@nbd.name>