sh: define PERF_COUNTER_INDEX_OFFSET.

Fixes up recent build breakage.
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

arch/sh/include/asm/perf_counter.h

@@ -4,4 +4,6 @@
 /* SH only supports software counters through this interface. */
 static inline void set_perf_counter_pending(void) {}
 
+#define PERF_COUNTER_INDEX_OFFSET	0
+
 #endif /* __ASM_SH_PERF_COUNTER_H */