xtensa:fix the incompatible pointer type warning in time.c

Fix the definition of the function ccount_read to be compatible
to the member read of the structure clocksource.
Signed-off-by: NWanlong Gao <wanlong.gao@gmail.com>
Signed-off-by: NChris Zankel <chris@zankel.net>

arch/xtensa/kernel/time.c

@@ -31,7 +31,7 @@ unsigned long ccount_per_jiffy;		/* per 1/HZ */
 unsigned long nsec_per_ccount;		/* nsec per ccount increment */
 #endif
 
-static cycle_t ccount_read(void)
+static cycle_t ccount_read(struct clocksource *cs)
 {
 	return (cycle_t)get_ccount();
 }