mt76: mt76x0e: another fix for the external PA current setting

- Use the register number define instead of a magic value
- Fix inverted bit test (override needs to be applied if the bit is not set)

Fixes: 2b2cb40b

 ("mt76x0: pci: add hw initialization at bootstrap")
Signed-off-by: Felix Fietkau <nbd@nbd.name>