kconfig: fix typo in XEN_SHSTK description

Rename 'vai' to 'via'.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Reviewed-by: Paul Durrant <paul@xen.org>
Release-acked-by: Paul Durrant <paul@xen.org>

xen/arch/x86/Kconfig

@@ -113,7 +113,7 @@ config XEN_SHSTK
 
 	  This option arranges for Xen to use CET-SS for its own protection.
 	  When CET-SS is active, 32bit PV guests cannot be used.  Backwards
-	  compatiblity can be provided vai the PV Shim mechanism.
+	  compatiblity can be provided via the PV Shim mechanism.
 
 config SHADOW_PAGING
         bool "Shadow Paging"