x86/xen: fix non-ANSI declaration of xen_has_pv_devices()

x86/xen: fix non-ANSI declaration of xen_has_pv_devices()

xen_has_pv_devices() has no parameters, so use the normal void
parameter convention to make it match the prototype in the header file
include/xen/platform_pci.h.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
(cherry picked from commit 772f95e3b9460c64fb99b134022855cbce75b9a0)
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
(cherry picked from commit b19b9231523ba06c961a3807f58814fd8071d176)