[media] atmel-isi: code cleanup

Ensure that ISI is clocked before starting sensor sub device.
Remove un-needed type check in try_fmt().
Use clamp() macro for hardware capabilities.
Fix wrong tabulation to space.

Signed-off-by: Hugues Fruchet <hugues.fruchet@st.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>