proc: faster /proc/cmdline

Use seq_puts() and skip format string processing.

Link: http://lkml.kernel.org/r/20180309222948.GB3843@avx2
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/proc/cmdline.c

@@ -6,7 +6,8 @@
 
 static int cmdline_proc_show(struct seq_file *m, void *v)
 {
-	seq_printf(m, "%s\n", saved_command_line);
+	seq_puts(m, saved_command_line);
+	seq_putc(m, '\n');
 	return 0;
 }