brcmsmac: avoid calling set_txpwr_by_index() twice

For lcnphy revision 1 or when hardware supports i/q calibration the
function wlc_lcnphy_set_txpwr_by_index() was called twice.

Tested-by: David Herrmann <dh.herrmann@gmail.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>