perf block-info: Fix wrong block address comparison in block_info__cmp()

perf block-info: Fix wrong block address comparison in block_info__cmp()

Commit 6041441870ab ("perf block: Cleanup and refactor block info
functions") introduces block_info__cmp(), which compares two blocks.

But the issues are:

1. It should return the strcmp cmp value only if it's not 0.

2. When symbol names are matched, we need to compare the addresses
   of blocks further. But it wrongly uses the symbol addresses for
   comparison.

3. If the syms are both NULL, we can't consider these two blocks are
   matched.

This patch fixes above 3 issues.

Fixes: 6041441870ab ("perf block: Cleanup and refactor block info functions")
Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jin Yao <yao.jin@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20200202141655.32053-2-yao.jin@linux.intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>