package/xen: fix 'available' typo

Found by codespell.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Julien Olivain <ju.o@free.fr>
(cherry picked from commit 21e5a9a96b1c25a7d3a5e92fd405afb6aafde605)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/xen/Config.in

@@ -13,7 +13,7 @@ if BR2_PACKAGE_XEN
 config BR2_PACKAGE_XEN_HYPERVISOR
 	bool "Xen hypervisor"
 	help
-	  The Xen binaries are avaliable in /usr/lib/xen/ See
+	  The Xen binaries are available in /usr/lib/xen/ See
 	  http://wiki.xenproject.org/wiki/Getting_Started for using
 	  the Xen hypervisor.