isl/gen9: Fix slice offset calculation for 1D array images.
isl/gen9: Fix slice offset calculation for 1D array images.

The X component of the offset is set to the layer index times layer
height which is obviously bogus, return the vertical offset of the
slice as Y component instead.  Fixes a few image load/store tests that
use 1D arrays on SKL when forcing it to fall back to untyped reads and
writes.

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler