usb: typec: tcpm: turn tcpm_ams_finish into void function

This function always return '0' and no callers use the return value.
So make it a void function.

This eliminates the following coccicheck warning:
./drivers/usb/typec/tcpm/tcpm.c:778:5-8: Unneeded variable: "ret".
Return "0" on line 794

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Link: https://lore.kernel.org/r/1615185330-118246-1-git-send-email-yang.lee@linux.alibaba.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/typec/tcpm/tcpm.c

@@ -780,10 +780,8 @@ static enum typec_cc_status tcpm_rp_cc(struct tcpm_port *port)
 	return TYPEC_CC_RP_DEF;
 }
 
-static int tcpm_ams_finish(struct tcpm_port *port)
+static void tcpm_ams_finish(struct tcpm_port *port)
 {
-	int ret = 0;
-
 	tcpm_log(port, "AMS %s finished", tcpm_ams_str[port->ams]);
 
 	if (port->pd_capable && port->pwr_role == TYPEC_SOURCE) {
@@ -797,8 +795,6 @@ static int tcpm_ams_finish(struct tcpm_port *port)
 
 	port->in_ams = false;
 	port->ams = NONE_AMS;
-
-	return ret;
 }
 
 static int tcpm_pd_transmit(struct tcpm_port *port,