tracing: Let filter_assign_type() detect FILTER_PTR_STRING

filter_assign_type() could detect dynamic string and static
string, but not string pointers. Teach filter_assign_type()
to detect string pointers, and this will be needed by trace
event injection code.

BTW, trace event hist uses FILTER_PTR_STRING too.
Link: http://lkml.kernel.org/r/20190525165802.25944-3-xiyou.wangcong@gmail.com

Cc: Ingo Molnar <mingo@redhat.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_events_filter.c

@@ -1080,6 +1080,9 @@ int filter_assign_type(const char *type)
 	if (strchr(type, '[') && strstr(type, "char"))
 		return FILTER_STATIC_STRING;
 
+	if (strcmp(type, "char *") == 0 || strcmp(type, "const char *") == 0)
+		return FILTER_PTR_STRING;
+
 	return FILTER_OTHER;
 }