tracing/dynevent: Fix a memory leak in an error handling path

We must free 'argv' before returning, as already done in all the other
paths of this function.

Link: https://lkml.kernel.org/r/21e3594ccd7fc88c5c162c98450409190f304327.1618136448.git.christophe.jaillet@wanadoo.fr

Fixes: d262271d

 ("tracing/dynevent: Delegate parsing to create function")
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>