printk: fix discarding message when recursion_bug

Impact: fix truncated recursion bug message printout

When recursion_bug is true, kernel discards original message because printk_buf
contains recursion_bug_msg with NULL terminator. The sizeof(recursion_bug_msg)
makes this, use strlen() to get correct length without NULL terminator.
Reported-by: Toshikazu Nakayama <nakayama.ts@ncos.nec.co.jp>
Signed-off-by: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/printk.c

@@ -662,7 +662,7 @@ asmlinkage int vprintk(const char *fmt, va_list args)
 	if (recursion_bug) {
 		recursion_bug = 0;
 		strcpy(printk_buf, recursion_bug_msg);
-		printed_len = sizeof(recursion_bug_msg);
+		printed_len = strlen(recursion_bug_msg);
 	}
 	/* Emit the output into the temporary buffer */
 	printed_len += vscnprintf(printk_buf + printed_len,