clk: pxa: Fix const discarding warning

A recent change to mark parent names as const missed this struct
member so we get warnings like:

drivers/clk/pxa/clk-pxa25x.c:122:2: warning: initialization
discards 'const' qualifier from pointer target type

Fix it.

Reported-by: kbuild test robot <[email protected]>
Acked-by: Uwe Kleine-König <[email protected]>
Signed-off-by: Stephen Boyd <[email protected]>
diff --git a/drivers/clk/pxa/clk-pxa.h b/drivers/clk/pxa/clk-pxa.h
index 7bf532d..d1de805 100644
--- a/drivers/clk/pxa/clk-pxa.h
+++ b/drivers/clk/pxa/clk-pxa.h
@@ -72,7 +72,7 @@
 	const char *name;
 	const char *dev_id;
 	const char *con_id;
-	const char **parent_names;
+	const char * const *parent_names;
 	struct clk_fixed_factor lp;
 	struct clk_fixed_factor hp;
 	struct clk_gate gate;