perf unwind: Fix unitialized 'offset' variable on aarch64

Commit dc2cf4ca ("perf unwind: Fix segbase for ld.lld linked
objects") uncovered the following issue on aarch64:

    util/unwind-libunwind-local.c: In function 'find_proc_info':
    util/unwind-libunwind-local.c:386:28: error: 'offset' may be used uninitialized in this function [-Werror=maybe-uninitialized]
    386 |                         if (ofs > 0) {
        |                            ^
    util/unwind-libunwind-local.c:199:22: note: 'offset' was declared here
    199 |         u64 address, offset;
        |                      ^~~~~~
    util/unwind-libunwind-local.c:371:20: error: 'offset' may be used uninitialized in this function [-Werror=maybe-uninitialized]
    371 |                 if (ofs <= 0) {
        |                    ^
    util/unwind-libunwind-local.c:199:22: note: 'offset' was declared here
    199 |         u64 address, offset;
        |                      ^~~~~~
    util/unwind-libunwind-local.c:363:20: error: 'offset' may be used uninitialized in this function [-Werror=maybe-uninitialized]
    363 |                 if (ofs <= 0) {
        |                    ^
    util/unwind-libunwind-local.c:199:22: note: 'offset' was declared here
    199 |         u64 address, offset;
        |                      ^~~~~~
    In file included from util/libunwind/arm64.c:37:

Fixes: dc2cf4ca ("perf unwind: Fix segbase for ld.lld linked objects")
Signed-off-by: Ivan Babrou <ivan@cloudflare.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Fangrui Song <maskray@google.com>
Cc: Ian Rogers <irogers@google.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: kernel-team@cloudflare.com
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20220701182046.12589-1-ivan@cloudflare.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/unwind-libunwind-local.c

@@ -197,7 +197,7 @@ static int elf_section_address_and_offset(int fd, const char *name, u64 *address
 #ifndef NO_LIBUNWIND_DEBUG_FRAME
 static u64 elf_section_offset(int fd, const char *name)
 {
-	u64 address, offset;
+	u64 address, offset = 0;
 
 	if (elf_section_address_and_offset(fd, name, &address, &offset))
 		return 0;