tty: serial: Fix spelling mistake "Asychronous" -> "Asynchronous"

There is a spelling mistake in the Kconfig text. Fix it.
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/20210719102421.14813-1-colin.king@canonical.comSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/Kconfig

@@ -1382,7 +1382,7 @@ config SERIAL_ST_ASC
 	select SERIAL_CORE
 	depends on ARM || COMPILE_TEST
 	help
-	  This driver is for the on-chip Asychronous Serial Controller on
+	  This driver is for the on-chip Asynchronous Serial Controller on
 	  STMicroelectronics STi SoCs.
 	  ASC is embedded in ST COMMS IP block. It supports Rx & Tx functionality.
 	  It support all industry standard baud rates.