mt76: mt7915: Remove unneeded semicolon

fix semicolon.cocci warnings:
drivers/net/wireless/mediatek/mt76/mt7915/mac.c:1694:2-3: Unneeded semicolon

Signed-off-by: Xu Wang <vulab@iscas.ac.cn>
Signed-off-by: Felix Fietkau <nbd@nbd.name>