anv: call blob_finish when done with it

anv: call blob_finish when done with it

Fixes leaks from anv_device_upload_nir:

  ==7345== 8,192 bytes in 2 blocks are definitely lost in loss record 24 of 24
  ==7345==    at 0x4C2ED78: malloc (vg_replace_malloc.c:308)
  ==7345==    by 0x4C31393: realloc (vg_replace_malloc.c:836)
  ==7345==    by 0x54E0848: grow_to_fit (blob.c:67)
  ==7345==    by 0x54E0BE5: blob_reserve_bytes (blob.c:166)
  ==7345==    by 0x54E0C7C: blob_reserve_intptr (blob.c:186)
  ==7345==    by 0x54704A7: nir_serialize (nir_serialize.c:1091)
  ==7345==    by 0x512F97D: anv_device_upload_nir (anv_pipeline_cache.c:756)

Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>