perf time-utils: Fix 32-bit nsec parsing

perf time-utils: Fix 32-bit nsec parsing

The "time utils" test fails in 32-bit builds:
  ...
  parse_nsec_time("18446744073.709551615")
  Failed. ptime 4294967295709551615 expected 18446744073709551615
  ...

Switch strtoul to strtoull as an unsigned long in 32-bit build isn't
64-bits.

Fixes: c284d669a20d408b ("perf tools: Move parse_nsec_time to time-utils.c")
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Cc: Chaitanya S Prakash <chaitanyas.prakash@arm.com>
Cc: Colin Ian King <colin.i.king@gmail.com>
Cc: David Ahern <dsa@cumulusnetworks.com>
Cc: Dominique Martinet <asmadeus@codewreck.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Garry <john.g.garry@oracle.com>
Cc: Junhao He <hejunhao3@huawei.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Yang Jihong <yangjihong@bytedance.com>
Link: https://lore.kernel.org/r/20240831070415.506194-3-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>