anv/blorp: make anv_cmd_buffer_alloc_blorp_binding_table() return a VkResult

anv/blorp: make anv_cmd_buffer_alloc_blorp_binding_table() return a VkResult

Instead of asserting inside the function, and then use use that information
to return early from its callers upon failure.

v2:
  - Make sure that clear_color_attachment() and
    clear_depth_stencil_attachment() get the VkResult as well so they
    avoid executing the batch if an error happened. (Topi)

Reviewed-by: Topi Pohjolainen <topi.pohjolainen@intel.com>