perf vendor events powerpc: Fix spelling mistake "icach" -> "icache"

There is a spelling mistake in the description text, fix it.

Signed-off-by: Colin King <[e-mail]>
Acked-by: Ian Rogers <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: [e-mail]
Link: http://lore.kernel.org/lkml/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/pmu-events/arch/powerpc/power8/other.json

···
   {
     "EventCode": "0x4e010",
     "EventName": "PM_GCT_NOSLOT_IC_L3MISS",
-    "BriefDescription": "Gct empty for this thread due to icach l3 miss",
+    "BriefDescription": "Gct empty for this thread due to icache l3 miss",
     "PublicDescription": ""
   },
   {