sh: make set_perf_counter_pending() static inline.

Fixes up a recently introduced build error.
Reported-by: Kyle McMartin <kyle@mcmartin.ca>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/include/asm/perf_counter.h

@@ -2,6 +2,6 @@
 #define __ASM_SH_PERF_COUNTER_H
 
 /* SH only supports software counters through this interface. */
-#define set_perf_counter_pending()	do { } while (0)
+static inline void set_perf_counter_pending(void) {}
 
 #endif /* __ASM_SH_PERF_COUNTER_H */