Staging: speakup: Fix getting port information

Commit f79b0d9c ("staging: speakup: Fixed warning <linux/serial.h>
instead of <asm/serial.h>") broke the port information in the speakup
driver: SERIAL_PORT_DFNS only gets defined if asm/serial.h is included,
and no other header includes asm/serial.h.

We here make sure serialio.c does get the arch-specific definition of
SERIAL_PORT_DFNS from asm/serial.h, if any.

Along the way, this makes sure that we do have information for the
requested serial port number (index)

Fixes: f79b0d9c ("staging: speakup: Fixed warning <linux/serial.h> instead of <asm/serial.h>")
Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Cc: stable <stable@vger.kernel.org> # 3.18
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/speakup/serialio.c

@@ -6,6 +6,11 @@
 #include "spk_priv.h"
 #include "serialio.h"
 
+#include <linux/serial_core.h>
+/* WARNING:  Do not change this to <linux/serial.h> without testing that
+ * SERIAL_PORT_DFNS does get defined to the appropriate value. */
+#include <asm/serial.h>
+
 #ifndef SERIAL_PORT_DFNS
 #define SERIAL_PORT_DFNS
 #endif
@@ -23,9 +28,15 @@ const struct old_serial_port *spk_serial_init(int index)
 	int baud = 9600, quot = 0;
 	unsigned int cval = 0;
 	int cflag = CREAD | HUPCL | CLOCAL | B9600 | CS8;
-	const struct old_serial_port *ser = rs_table + index;
+	const struct old_serial_port *ser;
 	int err;
 
+	if (index >= ARRAY_SIZE(rs_table)) {
+		pr_info("no port info for ttyS%d\n", index);
+		return NULL;
+	}
+	ser = rs_table + index;
+
 	/*	Divisor, bytesize and parity */
 	quot = ser->baud_base / baud;
 	cval = cflag & (CSIZE | CSTOPB);