Fix ia64 compilation IS_ERR and PTE_ERR errors.

When building ia64 kernel with CONFIG_XEN_SYS_HYPERVISOR, compiler reports
errors:

drivers/xen/sys-hypervisor.c: In function ‘uuid_show’:
drivers/xen/sys-hypervisor.c:125: error: implicit declaration of function ‘IS_ERR’
drivers/xen/sys-hypervisor.c:126: error: implicit declaration of function ‘PTR_ERR’

This patch fixes the errors.
Signed-off-by: NFenghua Yu <fenghua.yu@intel.com>
Acked-by: NIsaku Yamahata <yamahata@valinux.co.jp>

arch/ia64/include/asm/xen/hypervisor.h

@@ -33,6 +33,7 @@
 #ifndef _ASM_IA64_XEN_HYPERVISOR_H
 #define _ASM_IA64_XEN_HYPERVISOR_H
 
+#include <linux/err.h>
 #include <xen/interface/xen.h>
 #include <xen/interface/version.h>	/* to compile feature.c */
 #include <xen/features.h>		/* to comiple xen-netfront.c */