imagemagick: disable opencl

* it can try to use host paths like:
  -lOpenCL -L/usr/lib/nvidia
  -lCL -L/usr/lib/nvidia
  -lclparser -L/usr/lib/nvidia
  ERROR: This autoconf log indicates errors, it looked at host include and/or library paths while determining system capabilities.

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>