[S390] update documentation for hvc_iucv kernel parameter.

Signed-off-by: NHendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

Documentation/kernel-parameters.txt

@@ -829,8 +829,8 @@ and is between 256 and 4096 characters. It is defined in the file
 
 	hlt		[BUGS=ARM,SH]
 
-	hvc_iucv=	[S390] Number of z/VM IUCV Hypervisor console (HVC)
-			       back-ends. Valid parameters: 0..8
+	hvc_iucv=	[S390] Number of z/VM IUCV hypervisor console (HVC)
+			       terminal devices. Valid values: 0..8
 
 	i8042.debug	[HW] Toggle i8042 debug mode
 	i8042.direct	[HW] Put keyboard port into non-translated mode