serial: earlycon: Skip parse_options() if empty string

Earlycon param strings of the form
   earlycon=<name>
are rejected from parse_options() with an error (which, in turn,
results in a NULL argument for the setup() method options parameter).

Only pass non-empty string to parse_options(); this will enable
handling actual parse errors differently than expected and allow
formats.
Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/earlycon.c

@@ -109,13 +109,16 @@ int __init setup_earlycon(char *buf, const char *match,
 	len = strlen(match);
 	if (strncmp(buf, match, len))
 		return 0;
-	if (buf[len] && (buf[len] != ','))
-		return 0;
 
-	buf += len + 1;
+	if (buf[len]) {
+		if (buf[len] != ',')
+			return 0;
+		buf += len + 1;
+	} else
+		buf = NULL;
 
 	/* On parsing error, pass the options buf to the setup function */
-	if (!parse_options(&early_console_dev, buf))
+	if (buf && !parse_options(&early_console_dev, buf))
 		buf = NULL;
 
 	port->uartclk = BASE_BAUD * 16;