perf symbols: Fix kernel maps for kcore and eBPF

Adjust 'map->pgoff' also when moving a map's start address.

Example with v5.4.34 based kernel:

  Before:

    $ sudo tools/perf/perf record -a --kcore -e intel_pt//k sleep 1
    [ perf record: Woken up 1 times to write data ]
    [ perf record: Captured and wrote 1.958 MB perf.data ]
    $ sudo tools/perf/perf script --itrace=e >/dev/null
    Warning:
    961 instruction trace errors

  After:

    $ sudo tools/perf/perf script --itrace=e >/dev/null
    $

Committer testing:

  # uname -a
  Linux seventh 5.6.10-100.fc30.x86_64 #1 SMP Mon May 4 15:36:44 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
  #

Before:

  # perf record -a --kcore -e intel_pt//k sleep 1
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.923 MB perf.data ]
  # perf script --itrace=e >/dev/null
  Warning:
  295 instruction trace errors
  #

After:

  # perf record -a --kcore -e intel_pt//k sleep 1
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.919 MB perf.data ]
  # perf script --itrace=e >/dev/null
  #

Fixes: fb5a88d ("perf tools: Preserve eBPF maps when loading kcore")
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: stable@vger.kernel.org
Link: http://lore.kernel.org/lkml/20200602112505.1406-1-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/symbol.c

@@ -1224,6 +1224,7 @@ int maps__merge_in(struct maps *kmaps, struct map *new_map)
 
 				m->end = old_map->start;
 				list_add_tail(&m->node, &merged);
+				new_map->pgoff += old_map->end - new_map->start;
 				new_map->start = old_map->end;
 			}
 		} else {
@@ -1244,6 +1245,7 @@ int maps__merge_in(struct maps *kmaps, struct map *new_map)
 				 *      |new......| ->         |new...|
 				 * |old....|        -> |old....|
 				 */
+				new_map->pgoff += old_map->end - new_map->start;
 				new_map->start = old_map->end;
 			}
 		}