perf callchain: Fix compilation on powerpc with gcc11+

Got following build fail on powerpc:

    CC      arch/powerpc/util/skip-callchain-idx.o
  In function ‘check_return_reg’,
      inlined from ‘check_return_addr’ at arch/powerpc/util/skip-callchain-idx.c:213:7,
      inlined from ‘arch_skip_callchain_idx’ at arch/powerpc/util/skip-callchain-idx.c:265:7:
  arch/powerpc/util/skip-callchain-idx.c:54:18: error: ‘dwarf_frame_register’ accessing 96 bytes \
  in a region of size 64 [-Werror=stringop-overflow=]
     54 |         result = dwarf_frame_register(frame, ra_regno, ops_mem, &ops, &nops);
        |                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  arch/powerpc/util/skip-callchain-idx.c: In function ‘arch_skip_callchain_idx’:
  arch/powerpc/util/skip-callchain-idx.c:54:18: note: referencing argument 3 of type ‘Dwarf_Op *’
  In file included from /usr/include/elfutils/libdwfl.h:32,
                   from arch/powerpc/util/skip-callchain-idx.c:10:
  /usr/include/elfutils/libdw.h:1069:12: note: in a call to function ‘dwarf_frame_register’
   1069 | extern int dwarf_frame_register (Dwarf_Frame *frame, int regno,
        |            ^~~~~~~~~~~~~~~~~~~~
  cc1: all warnings being treated as errors

The dwarf_frame_register args changed with [1],
Updating ops_mem accordingly.

[1] https://sourceware.org/git/?p=elfutils.git;a=commit;h=5621fe5443da23112170235dd5cac161e5c75e65

Reviewed-by: Kajol Jain <kjain@linux.ibm.com>
Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Acked-by: Mark Wieelard <mjw@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Link: https://lore.kernel.org/r/20210928195253.1267023-1-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Author: Jiri Olsa

tools/perf/arch/powerpc/util/skip-callchain-idx.c

@@ -45,7 +45,7 @@ static const Dwfl_Callbacks offline_callbacks = {
  */
 static int check_return_reg(int ra_regno, Dwarf_Frame *frame)
 {
-	Dwarf_Op ops_mem[2];
+	Dwarf_Op ops_mem[3];
 	Dwarf_Op dummy;
 	Dwarf_Op *ops = &dummy;
 	size_t nops;