staging: brcm80211: flatten wlc_phy_shared_detach()

wlc_phy_shared_detach() is an unnecessary level of indirection to just
call kfree(), so replace the function with kfree().

Signed-off-by: Henry Ptasinski <henryp@broadcom.com>
Reviewed-by: Roland Vossen <rvossen@broadcom.com>
Reviewed-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>