tracing: Remove redundant assignment to event_var

Variable event_var is set to 'ERR_PTR(-EINVAL)', but this value
is never read as it is overwritten or not used later on, hence
it is a redundant assignment and can be removed.

Clean up the following clang-analyzer warning:

kernel/trace/trace_events_hist.c:2437:21: warning: Value stored to
'event_var' during its initialization is never read
[clang-analyzer-deadcode.DeadStores].

Link: https://lkml.kernel.org/r/1620470236-26562-1-git-send-email-jiapeng.chong@linux.alibaba.comReported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_events_hist.c

@@ -2434,12 +2434,12 @@ create_field_var_hist(struct hist_trigger_data *target_hist_data,
 		      char *subsys_name, char *event_name, char *field_name)
 {
 	struct trace_array *tr = target_hist_data->event_file->tr;
-	struct hist_field *event_var = ERR_PTR(-EINVAL);
 	struct hist_trigger_data *hist_data;
 	unsigned int i, n, first = true;
 	struct field_var_hist *var_hist;
 	struct trace_event_file *file;
 	struct hist_field *key_field;
+	struct hist_field *event_var;
 	char *saved_filter;
 	char *cmd;
 	int ret;