wifi: mt76: mt7915: workaround dubious x | !y warning

Sparse warns:

drivers/net/wireless/mediatek/mt76/mt7915/debugfs.c:526:9: warning: dubious: x | !y

Workaround it by using the '?' operator. Compile tested only.

Signed-off-by: Kalle Valo <kvalo@kernel.org>
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://msgid.link/20240325155838.1558680-1-kvalo@kernel.org