xvkbd: remove version from the patch file name

The version in xvkbd patch file name doesn't patch the version of the
package, so use the new convention that consists in not having the
package version in the patch file names.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>