perf record: Fix memory leak when using '--user-regs=?' to list registers

When using 'perf record's option '-I' or '--user-regs=' along with
argument '?' to list available register names, memory of variable 'os'
allocated by strdup() needs to be released before __parse_regs()
returns, otherwise memory leak will occur.

Fixes: bcc84ec65ad1 ("perf record: Add ability to name registers to record")
Signed-off-by: Zheng Zengkai <[e-mail]>
Acked-by: Jiri Olsa <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Li Bin <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/parse-regs-options.c

···
 #endif
 				fputc('\n', stderr);
 				/* just printing available regs */
-				return -1;
+				goto error;
 			}
 #ifdef HAVE_PERF_REGS_SUPPORT
 			for (r = sample_reg_masks; r->name; r++) {