libtracefs: Fix enum type in read_event_state

The state variable is of type event_state but is assigned
TRACEFS_ERROR(-1) of type tracefs_enable_state which has no
corresponding event_state name. Fix this by assigning STATE_ERROR(4).

Link: https://lore.kernel.org/20250530225426.721741-1-irogers@google.com
Reported-by: Asmaa AbdelGhany <asmok@google.com>
Signed-off-by: Ian Rogers <irogers@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>