v3d: Fix predication with atomic image operations

Fixes dEQP test:
dEQP-GLES31.functional.synchronization.inter_call.with_memory_barrier.image_atomic_multiple_interleaved_write_read

Fixes piglit test:
spec/glsl-es-3.10/execution/cs-image-atomic-if-else.shader_test

Fixes: 6281f26f ("v3d: Add support for shader_image_load_store.")

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
(cherry picked from commit d9830551)