tty: amiserial: Fix comment typo

The double `should' is duplicated in line 15, remove one.

Signed-off-by: Jason Wang <wangborong@cdjrlc.com>
Link: https://lore.kernel.org/r/20220715054401.9870-1-wangborong@cdjrlc.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/amiserial.c

@@ -12,7 +12,7 @@
  * (non hardware specific) changes to serial.c.
  *
  * The port is registered with the tty driver as minor device 64, and
- * therefore other ports should should only use 65 upwards.
+ * therefore other ports should only use 65 upwards.
  *
  * Richard Lucock 28/12/99
  *