mwl8k: Move tx/rx antenna configuration to mwl8k_probe_hw

This avoids calling mwl8k_cmd_rf_antenna functions every
time mwl8k_config function is called.

Signed-off-by: Yogesh Ashok Powar <yogeshp@marvell.com>
Signed-off-by: Nishant Sarmukadam <nishants@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>