perf ftrace: Fix hashmap__new() error checking

perf ftrace: Fix hashmap__new() error checking

The hashmap__new() function never returns NULL, it returns error
pointers. Fix the error checking to match.

Additionally, set ftrace->profile_hash to NULL on error, and return the
exact error code from hashmap__new().

Fixes: 0f223813edd051a5 ("perf ftrace: Add 'profile' command")
Suggested-by: Ian Rogers <irogers@google.com>
Signed-off-by: Chen Ni <nichen@iscas.ac.cn>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>