tracing: Fix logged instance name on creation failure

tracing: Fix logged instance name on creation failure

When boot instance creation fails, the kernel incorrectly logs "(null)"
as the instance name because strsep() consumes curr_str entirely during
parsing.

Print the properly parsed name variable instead. And while at it log
the error code.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260807085423.4175161-1-vdonnefort@google.com
Fixes: cb1f98c5e574 ("tracing: Add creation of instances at boot command line")
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>