x86: earlyprintk: Fix regression to handle serial,ttySn as 1 arg

Commit c953094 ("early_printk: Allow more than one early console")
introduced a regression in the parsing of the earlyprintk= kernel
arguments.

If you specify "earlyprintk=serial,ttyS0,115200" as a kernel
argument, the "serial,ttyS" should be parsed as a single argument
and not as "serial" and then "ttyS".

Also update the documentation to reflect you can specify the ttyS
directly without the "serial" argument.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Cc: Len Brown <lenb@kernel.org>
Cc: Greg KH <gregkh@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
LKML-Reference: <4ABB7D5E.6000301@windriver.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

Documentation/kernel-parameters.txt

@@ -671,6 +671,7 @@ and is between 256 and 4096 characters. It is defined in the file
 	earlyprintk=	[X86,SH,BLACKFIN]
 			earlyprintk=vga
 			earlyprintk=serial[,ttySn[,baudrate]]
+			earlyprintk=ttySn[,baudrate]
 			earlyprintk=dbgp[debugController#]
 
 			Append ",keep" to not disable it when the real console

arch/x86/kernel/early_printk.c

@@ -206,8 +206,11 @@ static int __init setup_early_printk(char *buf)
 
 	while (*buf != '\0') {
 		if (!strncmp(buf, "serial", 6)) {
-			early_serial_init(buf + 6);
+			buf += 6;
+			early_serial_init(buf);
 			early_console_register(&early_serial_console, keep);
+			if (!strncmp(buf, ",ttyS", 5))
+				buf += 5;
 		}
 		if (!strncmp(buf, "ttyS", 4)) {
 			early_serial_init(buf + 4);