intel/vec4: Set channel_sizes for MOV_INDIRECT sources

Otherwise, any indirect push constant access results in an assertion
failure when we start digging through the channel_sizes array.  This
fixes dEQP-VK.pipeline.push_constant.graphics_pipeline.dynamic_index_vert
on Haswell.  It should be a harmless no-op for GL since indirect push
constants aren't used there.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Fixes: e69e5c70 "i965/vec4: load dvec3/4 uniforms first in the..."
(cherry picked from commit 2b977989)