The real maximum was `GPU_SAMPLER_ICON`, not `GPU_SAMPLER_REPEAT`, my
bad. {rBa31a87f8943aa40}
Move `GPU_SAMPLER_MAX` out of the enum since it's used as an `int`
at many places.
Also, the macro `ENUM_OPERATORS` needs a maximum, and this enumerator
cannot be used as the argument of that macro. It creates wrong values
in the `~` NOT operator.
Thanks @deadpin for catching this.
Reviewed By: fclem
Differential Revision: https://developer.blender.org/D9157
83e91485d0