wifi: mt76: Remove redundant assignment to variable tidno

The variable tidno is being assigned a value that is not being read
and is being re-assigned a new value a few statements later.
The assignment is redundant and can be removed.

Cleans up clang scan warning:
drivers/net/wireless/mediatek/mt76/agg-rx.c:125:5: warning: Value stored
to 'tidno' during its initialization is never read [deadcode.DeadStores]

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>