dt-bindings: media: st,stmipid02: correct lane-polarities maxItems

The MIPID02 can use up to 2 data lanes which leads to having a maximum
item number of 3 for the lane-polarities since this also contains the
clock lane.

CC: stable@vger.kernel.org
Fixes: c2741cbe ("dt-bindings: media: st,stmipid02: Convert the text bindings to YAML")
Signed-off-by: Alain Volmat <alain.volmat@foss.st.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>