tmp105: Read temperature in milli-celsius

tmp105: Read temperature in milli-celsius

Right now, the temperature property must be written in milli-celsius,
but it reads back the value in 8.8 fixed point.  Fix this by letting the
property read back the original value (possibly rounded).  Also simplify
the code that does the conversion.

Before:

    (QEMU) qom-set path=/machine/peripheral/sensor property=temperature value=20000
    {u'return': {}}
    (QEMU) qom-get path=sensor property=temperature
    {u'return': 5120}

After:

    (QEMU) qom-set path=/machine/peripheral/sensor property=temperature value=20000
    {u'return': {}}
    (QEMU) qom-get path=sensor property=temperature
    {u'return': 20000}

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>