wifi: mt76: mt7996: remove unnecessary key->cipher check for BIP frames

The cipher type check is redundant, and there is no need to dereference the
key struct here.

Signed-off-by: Michael-CY Lee <michael-cy.lee@mediatek.com>
Link: https://patch.msgid.link/20250311103646.43346-3-nbd@nbd.name


Signed-off-by: Felix Fietkau <nbd@nbd.name>