tracing/filters: Fix error-handling of cpulist parsing buffer

tracing/filters: Fix error-handling of cpulist parsing buffer

parse_pred() allocates a string buffer to parse the user-provided cpulist,
but doesn't check the allocation result nor does it free the buffer once it
is no longer needed.

Add an allocation check, and free the buffer as soon as it is no longer
needed.

Link: https://lkml.kernel.org/r/20230901151039.125186-2-vschneid@redhat.com
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Reported-by: Steven Rostedt <rostedt@goodmis.org>
Reported-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Valentin Schneider <vschneid@redhat.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>