xen: relax signature check

Some versions of Xen 3.x set their magic number to "xen-3.[12]", so
relax the test to match them.
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

arch/x86/xen/enlighten.c

@@ -1131,7 +1131,7 @@ asmlinkage void __init xen_start_kernel(void)
 	if (!xen_start_info)
 		return;
 
-	BUG_ON(memcmp(xen_start_info->magic, "xen-3.0", 7) != 0);
+	BUG_ON(memcmp(xen_start_info->magic, "xen-3", 5) != 0);
 
 	/* Install Xen paravirt ops */
 	pv_info = xen_info;