serial: max310x: Fix devicetree documentation for clock name

Clock names mistakenly given opposite. This patch fix this issue.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/serial/maxim,max310x.txt

@@ -13,8 +13,8 @@ Required properties:
   controller. The format of the interrupt specifier depends on the
   parent interrupt controller.
 - clocks: phandle to the IC source clock.
-- clock-names: Should be "osc" if clock is an external crystal or
-  "xtal" if an external clock source is used.
+- clock-names: Should be "xtal" if clock is an external crystal or
+  "osc" if an external clock source is used.
 
 Optional properties:
 - gpio-controller: Marks the device node as a GPIO controller.