wifi: mt76: Remove an unneeded local variable in mt76x02_dma_init()

Remove 't' which is unneeded since commit f3950a41 ("mt76: set
txwi_size according to the driver value")

This slightly simplifies the code.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://patch.msgid.link/e86d5602bdd8b6bd22258ee69536992f39470bf5.1744928865.git.christophe.jaillet@wanadoo.fr


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