perf report: Fix sample number stats for branch entry mode

perf report: Fix sample number stats for branch entry mode

Currently, stats->nr_samples is incremented per entry in the branch stack
instead of per sample taken. As a result, statistics of samples taken
during perf record in --branch-filter or --branch-any mode does not
seem correct. Instead call hists__inc_nr_samples() for each sample taken
instead of for each entry in the branch stack.

Before:

$ ./perf record -e cycles:u -b -c 10000000000 ./tchain_edit
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.005 MB perf.data (2 samples) ]
$ perf report -D | tail -n 16
Aggregated stats:
               TOTAL events:         16
                COMM events:          2  (12.5%)
                EXIT events:          1  ( 6.2%)
              SAMPLE events:          2  (12.5%)
               MMAP2 events:          2  (12.5%)
             KSYMBOL events:          1  ( 6.2%)
      FINISHED_ROUND events:          1  ( 6.2%)
            ID_INDEX events:          1  ( 6.2%)
          THREAD_MAP events:          1  ( 6.2%)
             CPU_MAP events:          1  ( 6.2%)
        EVENT_UPDATE events:          2  (12.5%)
           TIME_CONV events:          1  ( 6.2%)
       FINISHED_INIT events:          1  ( 6.2%)
cpu_core/cycles/u stats:
              SAMPLE events:         64

After:

$ ./perf report -D | tail -n 16
Aggregated stats:
               TOTAL events:         16
                COMM events:          2  (12.5%)
                EXIT events:          1  ( 6.2%)
              SAMPLE events:          2  (12.5%)
               MMAP2 events:          2  (12.5%)
             KSYMBOL events:          1  ( 6.2%)
      FINISHED_ROUND events:          1  ( 6.2%)
            ID_INDEX events:          1  ( 6.2%)
          THREAD_MAP events:          1  ( 6.2%)
             CPU_MAP events:          1  ( 6.2%)
        EVENT_UPDATE events:          2  (12.5%)
           TIME_CONV events:          1  ( 6.2%)
       FINISHED_INIT events:          1  ( 6.2%)
cpu_core/cycles/u stats:
              SAMPLE events:          2

Signed-off-by: Thomas Falcon <thomas.falcon@intel.com>
Link: https://lore.kernel.org/r/20250220045942.114965-1-thomas.falcon@intel.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>