i965/fs: Clamp image array indices to the array bounds on IVB.

i965/fs: Clamp image array indices to the array bounds on IVB.

This fixes the spec@arb_shader_image_load_store@invalid index bounds
piglit tests on IVB, which were causing a GPU hang and then a crash
due to the invalid binding table index result of the array index
calculation.  Other generations seem to behave sensibly when an
invalid surface is provided so it doesn't look like we need to care.

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Chris Forbes <chrisf@ijw.co.nz>