perf maps: Fixup maps_by_name when modifying maps_by_address

perf maps: Fixup maps_by_name when modifying maps_by_address

We can't just replacing the map in the maps_by_address and not touching
on the maps_by_name, that would leave the refcount as 1 and thus trip
another consistency check, this one:

  perf: util/maps.c:110: check_invariants:
  	Assertion `refcount_read(map__refcnt(map)) > 1' failed.

  106         /*
  107          * Maps by name maps should be in maps_by_address, so
  108          * the reference count should be higher.
  109          */
  110         assert(refcount_read(map__refcnt(map)) > 1);

Committer notice:

Initialize the newly added 'ni' variable, that really can't be
accessed unitialized trips some gcc versions, like:

  12    20.00 archlinux:base                : FAIL gcc version 13.2.1 20230801 (GCC)
    util/maps.c: In function ‘__maps__fixup_overlap_and_insert’:
    util/maps.c:896:54: error: ‘ni’ may be used uninitialized [-Werror=maybe-uninitialized]
      896 |                                 map__put(maps_by_name[ni]);
          |                                                      ^
    util/maps.c:816:25: note: ‘ni’ was declared here
      816 |         unsigned int i, ni;
          |                         ^~
    cc1: all warnings being treated as errors
    make[3]: *** [/git/perf-6.14.0-rc1/tools/build/Makefile.build:138: util] Error 2

Reported-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Reviewed-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/lkml/Z79std66tPq-nqsD@google.com
Link: https://lore.kernel.org/r/20250228211734.33781-5-acme@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>