brcm80211: smac: bugfix for tx mute in brcms_b_init()

Transmit can only be muted if the mac core is enabled. When brcms_b_init()
is called, the mac core is suspended. Brcms_b_init() calls a transmit mute
function that requires an enabled mac core. This code path is never taken,
but would have been taken in subsequent patches.

Reviewed-by: Alwin Beukers <alwin@broadcom.com>
Reviewed-by: Arend van Spriel <arend@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Roland Vossen <rvossen@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>