Use deposit32() rather than handcoded shifts/masks to update the
scratch registers. This is cleaner and incidentally avoids a clang
sanitizer complaint ("runtime error: left shift of 255 by 24 places
cannot be represented in type 'int'").
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>