[POWERPC] Fix ppc_rtas_progress_show()

Fixes the warning

	arch/powerpc/kernel/rtas-proc.c: In function 'ppc_rtas_progress_show':
	arch/powerpc/kernel/rtas-proc.c:382: warning: the address of
		'progress_led' will always evaluate as 'true'

by fixing the code to do what it presumably is meant to do.
Signed-off-by: Segher Boessenkool <segher@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/kernel/rtas-proc.c

@@ -379,7 +379,7 @@ static ssize_t ppc_rtas_progress_write(struct file *file,
 /* ****************************************************************** */
 static int ppc_rtas_progress_show(struct seq_file *m, void *v)
 {
-	if (progress_led)
+	if (progress_led[0])
 		seq_printf(m, "%s\n", progress_led);
 	return 0;
 }