spirv: Ignore ArrayStride in OpPtrAccessChain for Workgroup

spirv: Ignore ArrayStride in OpPtrAccessChain for Workgroup

From OpPtrAccessChain description in the SPIR-V spec (1.4 rev 1):

    For objects in the Uniform, StorageBuffer, or PushConstant storage
    classes, the element’s address or location is calculated using a
    stride, which will be the Base-type’s Array Stride when the Base
    type is decorated with ArrayStride. For all other objects, the
    implementation will calculate the element’s address or location.

For non-CL shaders the driver should layout the Workgroup storage
class, so override any explicitly set ArrayStride in the shader.  This
currently fixes only the lower_workgroup_access_to_offsets case, which
is used by anv.

Reviewed-by: Juan A. Suarez <jasuarez@igalia.com>