swiotlb-xen: remove BUG_ON in xen_bus_to_phys

swiotlb-xen: remove BUG_ON in xen_bus_to_phys

commit c884227eaae9936f8ecbde6e1387bccdab5f4e90 upstream.

On x86 truncation cannot occur because config XEN depends on X86_64 ||
(X86_32 && X86_PAE).

On ARM truncation can occur without CONFIG_ARM_LPAE, when the dma
operation involves foreign grants. However in that case the physical
address returned by xen_bus_to_phys is actually invalid (there is no mfn
to pfn tracking for foreign grants on ARM) and it is not used.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>