i965/wm: use binding size for ubo/ssbo when automatic size is unset

i965/wm: use binding size for ubo/ssbo when automatic size is unset

This fixes the same tests that commit 8cf2e892f was attempting to fix:

ES31-CTS.shader_storage_buffer_object.advanced-unsizedArrayLength-cs-std430-vec-bindrangeOffset
ES31-CTS.shader_storage_buffer_object.advanced-unsizedArrayLength-cs-std430-vec-bindrangeSize

as confirmed by Samuel.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Cc: Samuel Iglesias Gonsálvez <siglesias@igalia.com>
Cc: Marta Lofstedt <marta.lofstedt@intel.com>
Reviewed-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>