Arm/vGIC: adjust gicv3_its_deny_access() to fit other gic*_iomem_deny_access(

Arm/vGIC: adjust gicv3_its_deny_access() to fit other gic*_iomem_deny_access(

While an oversight in 9982fe275ba4 ("arm/vgic: drop const attribute
from gic_iomem_deny_access()"), the issue really became apparent only
when iomem_deny_access() was switched to have a non-const first
parameter.

Fixes: c4e5cc2ccc5b ("x86/ept: limit calls to memory_type_changed()")
Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Michal Orzel <michal.orzel@amd.com>
Tested-by: Michal Orzel <michal.orzel@amd.com>
Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>