media: i2c: alvium: fix alvium_get_fw_version()

Instead of reading device_fw reg as multiple regs let's read the entire
64bit reg using one i2c read and use bit masks and bit shifts to get fw
info.

Signed-off-by: Tommaso Merciai <tomm.merciai@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>