tracing: Clean up tb_fmt to not give faulty compile warning

gcc incorrectly states that the variable "fmt" is uninitialized when
CC_OPITMIZE_FOR_SIZE is set.

Instead of just blindly setting fmt to NULL, the code is cleaned up
a little to be a bit easier for humans to follow, as well as gcc
to know the variables are initialized.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace_printk.c

@@ -59,18 +59,19 @@ void hold_module_trace_bprintk_format(const char **start, const char **end)
 			continue;
 		}
 
+		fmt = NULL;
 		tb_fmt = kmalloc(sizeof(*tb_fmt), GFP_KERNEL);
-		if (tb_fmt)
+		if (tb_fmt) {
 			fmt = kmalloc(strlen(*iter) + 1, GFP_KERNEL);
-		if (tb_fmt && fmt) {
+			if (fmt) {
 				list_add_tail(&tb_fmt->list, &trace_bprintk_fmt_list);
 				strcpy(fmt, *iter);
 				tb_fmt->fmt = fmt;
-			*iter = tb_fmt->fmt;
-		} else {
+			} else
 				kfree(tb_fmt);
-			*iter = NULL;
 		}
+		*iter = fmt;
+
 	}
 	mutex_unlock(&btrace_mutex);
 }