media: i2c: imx296: fix error checking in imx296_read_temperature()

The "& IMX296_TMDOUT_MASK" means that "tmdout" can't be negative so the
error checking will not work.

Fixes: cb33db2b ("media: i2c: IMX296 camera sensor driver")
Signed-off-by: Dan Carpenter <error27@gmail.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>