KVM: SVM: remove unused variable dst_vaddr_end

Variable dst_vaddr_end is being assigned but is never used hence it is
redundant and can be removed.

Cleans up clang warning:
variable 'dst_vaddr_end' set but not used [-Wunused-but-set-variable]

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>