media: i2c: st-vgxy61: Move 'detect' call to 'power_on'

Previously the device detection was performed after patching.
Move it right after the reset to make sure we have the correct sensor
before trying to patch it.

Signed-off-by: Benjamin Mugnier <benjamin.mugnier@foss.st.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>