mt76: mt7915: fix aggr len debugfs node

mt76: mt7915: fix aggr len debugfs node

BugLink: https://bugs.launchpad.net/bugs/1929455
[ Upstream commit 9fb9d755fae20b5ad62ef8b4e9289e5baea2c6fc ]

Similar to mt7921, fix 802.11 aggr len debugfs reporting for mt7915 driver.

Fixes: e57b7901469fc ("mt76: add mac80211 driver for MT7915 PCIe-based chipsets")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kelsey Skunberg <kelsey.skunberg@canonical.com>