glsl: Update ir_variable::max_ifc_array_access properly.

glsl: Update ir_variable::max_ifc_array_access properly.

This patch modifies update_max_array_access() so that it updates
ir_variable::max_ifc_array_access to reflect the shader's use of
arrays appearing within interface blocks.

v2: Use an ordinary function in ast_array_index.cpp rather than a
virtual function in ir_rvalue.  Avoid dereferencing NULL when handling
accesses to ordinary structs.

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>