serial: Fix double word

Fix double word "start start" in comments.

Signed-off-by: Shaomin Deng <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/8250/8250_port.c

···
 	 * internal UARTs.
 	 * We're going to explicitly set the UUE bit to 0 before
 	 * trying to write and read a 1 just to make sure it's not
-	 * already a 1 and maybe locked there before we even start start.
+	 * already a 1 and maybe locked there before we even start.
 	 */
 	iersave = serial_in(up, UART_IER);
 	serial_out(up, UART_IER, iersave & ~UART_IER_UUE);