comedi: make all 'class' structures const

comedi: make all 'class' structures const

Now that the driver core allows for struct class to be in read-only
memory, making all 'class' structures to be declared at build time
placing them into read-only memory, instead of having to be dynamically
allocated at load time.

Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Cc: Ivan Orlov <ivan.orlov0322@gmail.com>
Cc: Xuezhi Zhang <zhangxuezhi1@coolpad.com>
Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ivan Orlov <ivan.orlov0322@gmail.com>
Link: https://lore.kernel.org/r/20230620144137.581406-2-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>