perf map: Delete two variable initialisations before null pointer checks in sort__sym_from_cmp()

Addresses of two data structure members were determined before
corresponding null pointer checks in the implementation of the function
“sort__sym_from_cmp”.

Thus avoid the risk for undefined behaviour by removing extra
initialisations for the local variables “from_l” and “from_r” (also
because they were already reassigned with the same value behind this
pointer check).

This issue was detected by using the Coccinelle software.

Fixes: 1b9e97a2

 ("perf tools: Fix report -F symbol_from for data without branch info")
Signed-off-by:  <elfring@users.sourceforge.net>
Acked-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: German Gomez <german.gomez@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/cocci/54a21fea-64e3-de67-82ef-d61b90ffad05@web.de/


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>