tty: serial: msm: Fix 'void function return statements are not generally useful' warning

fixed below checkpatch.pl warning:

WARNING: void function return statements are not generally useful
Signed-off-by: NKiran Padwal <kiran.padwal@smartplayin.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/msm_serial.c

@@ -787,8 +787,6 @@ static void msm_poll_put_char(struct uart_port *port, unsigned char c)
 
 	/* Enable interrupts */
 	msm_write(port, imr, UART_IMR);
-
-	return;
 }
 #endif