gigaset: return -ENOTTY for unimplemented functions

A number of functions in the usb_gigaset module will return -EINVAL if
CONFIG_GIGASET_UNDOCREQ is not set. Make these return -ENOTTY as it's
more specific and it might make it easier to see (from userspace) why
these functions actually fail.

Impact: some error return codes changed
Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Tilman Schmidt <tilman@imap.cc>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/isdn/gigaset/usb-gigaset.c

@@ -278,17 +278,17 @@ static int gigaset_set_line_ctrl(struct cardstate *cs, unsigned cflag)
 static int gigaset_set_modem_ctrl(struct cardstate *cs, unsigned old_state,
 				  unsigned new_state)
 {
-	return -EINVAL;
+	return -ENOTTY;
 }
 
 static int gigaset_set_line_ctrl(struct cardstate *cs, unsigned cflag)
 {
-	return -EINVAL;
+	return -ENOTTY;
 }
 
 static int gigaset_baud_rate(struct cardstate *cs, unsigned cflag)
 {
-	return -EINVAL;
+	return -ENOTTY;
 }
 #endif
 
@@ -577,7 +577,7 @@ static int gigaset_brkchars(struct cardstate *cs, const unsigned char buf[6])
 	return usb_control_msg(udev, usb_sndctrlpipe(udev, 0), 0x19, 0x41,
 			       0, 0, &buf, 6, 2000);
 #else
-	return -EINVAL;
+	return -ENOTTY;
 #endif
 }