mt76: fix header guard macro define names

The header guards that are #defined are different from those being
checked.  Fix this by #defining them to the correct name.

Fixes clang warnings:
drivers/net/wireless/mediatek/mt76/mt76x02_mcu.h:17:9:
warning: '__MT76x02_MCU_H' is used as a header guard here, followed
by #define of a different macro [-Wheader-guard]

drivers/net/wireless/mediatek/mt76/mt76x02_usb.h:17:9:
warning: '__MT76x02_USB_H' is used as a header guard here, followed
by #define of a different macro [-Wheader-guard]

Fixes: 905db747 ("mt76: usb: move mt76x02 mcu code in mt76x02-usb module")
Fixes: edaa580b ("mt76: move shared mcu_calibrate routine in mt76x02-lib module")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>