xen: sysfs: include err.h for PTR_ERR etc
xen: sysfs: include err.h for PTR_ERR etc

Fixes build error on ARM:
drivers/xen/sys-hypervisor.c: In function 'uuid_show_fallback':
drivers/xen/sys-hypervisor.c:127:2: error: implicit declaration of function 'IS_ERR' [-Werror=implicit-function-declaration]
drivers/xen/sys-hypervisor.c:128:3: error: implicit declaration of function 'PTR_ERR' [-Werror=implicit-function-declaration]

Acked-by: Stefano Stabellini <22a0c6385d750d07aa383c9f813cf6f0228657d8@eu.citrix.com>
Signed-off-by: Ian Campbell <9be92b3dbbd6611e3e4c9209fb3d04b4919e7cca@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <da3a51b335cef0eb0e2c329c5ef6bcd6acef687a@oracle.com>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs