Fix a call to userspace_mem_region_find to conform to its spec of
taking an inclusive, inclusive range. It was previously being called
with an inclusive, exclusive range. Also remove a redundant region bounds
check in vm_userspace_mem_region_add. Region overlap checking is already
performed by the call to userspace_mem_region_find.

Tested: Compiled tools/testing/selftests/kvm with -static
	Ran all resulting test binaries on an Intel Haswell test machine
	All tests passed
Signed-off-by: Ben Gardon <bgardon@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>