glsl/nir: do not change an element index to have correct block name

When SSBO array is used with packed layout, both IR tree
and as a result, NIR tree will be incorrect.
In fact, the SSBO dereference indices won't
match the array size in some cases like the following:

"layout(packed, binding=1) buffer SSBO { vec4 a; } ssbo[3];
 out vec4 color;
 void main() {
   color = ssbo[2].a;
 }"

After linking the IR and then NIR will have an SSBO array
definition with size 1 but dereference still will have index 2
and linked_shader->Program->sh.ShaderStorageBlocks
will contain just SSBO with name "SSBO[2]"

So this line should be removed at least as a workaround for now
to avoid error like:
Failed to find the block by name "SSBO[0]"

Fixes: 810dde2a "glsl/nir: Add a pass to lower UBO and SSBO access"
Signed-off-by: Andrii Simiklit <andrii.simiklit@globallogic.com>
Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>
(cherry picked from commit be6d51e1)