serial: msm: add lock annotation to msm_set_baud_rate()

msm_set_baud_rate() releases and re-acquires the port->lock, thus add
lock annotation for Sparse static code checks.
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230109152212.343476-1-krzysztof.kozlowski@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/msm_serial.c

@@ -1120,6 +1120,7 @@ msm_find_best_baud(struct uart_port *port, unsigned int baud,
 
 static int msm_set_baud_rate(struct uart_port *port, unsigned int baud,
 			     unsigned long *saved_flags)
+	__must_hold(&port->lock)
 {
 	unsigned int rxstale, watermark, mask;
 	struct msm_port *msm_port = to_msm_port(port);