staging: rtl8712: rtl871x_sta_mgt: Remove wrapper function

Remove wrapper function mfree_sta_priv_lock() that can be replaced by a
direct call to mfree_all_stainfo().

Signed-off-by: Amitoj Kaur Chawla <amitoj1606@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>