mt76: fix fix ampdu locking

mt76: fix fix ampdu locking

BugLink: https://bugs.launchpad.net/bugs/1906770
The current ampdu locking code does not unlock its mutex in the early
return case. This patch fixes it.

Signed-off-by: Markus Theil <markus.theil@tu-ilmenau.de>
Acked-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
(cherry picked from commit 05d6c8cfdbd6cefac6b373bad72775fcc4193c80)
Signed-off-by: Shrirang Bagul <shrirang.bagul@canonical.com>
Acked-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Ian May <ian.may@canonical.com>