glsl: reject size1x8 for image variable with floating-point data types
Fixes: 8d07d661 ("glsl,nir: Switch the enum representing shader image formats to PIPE_FORMAT.") Reviewed-by:Marek Olšák <marek.olsak@amd.com> Part-of: <mesa/mesa!5688> (cherry picked from commit 0c8873d8)