Two bits control TX power on BBP_R1 register. Correct the mask,
otherwise we clear additional bit on BBP_R1 register, what can have
unknown, possible negative effect.
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com> Signed-off-by: John W. Linville <linville@tuxdriver.com> Signed-off-by: Ben Hutchings <ben@decadent.org.uk>