media: atomisp: Rename __get_mipi_port() to atomisp_port_to_mipi_port()

media: atomisp: Rename __get_mipi_port() to atomisp_port_to_mipi_port()

Rename __get_mipi_port() to atomisp_port_to_mipi_port(), this is not a
private (not static) function so its name should be properly prefixed.

While at is also cleanup the weird handling of ATOMISP_CAMERA_PORT_TERTIARY
this seems to be a left over from when the driver also supported CSI
receivers with only 2 ports, but those are not supported by the current
code base, so this can be cleaned up now.

Link: https://lore.kernel.org/r/20230518153733.195306-5-hdegoede@redhat.com
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>