intel/fs/vec4: add missing dependency in write-on-write fixed GRFs

If we load constant data using pull constant SENDS, and we later load that register with some other data, we can end up in a situation where we don't track the initial fixed register write and therefore end up using uninitialized registers.

This tracks write-on-write of fixed GRFs like we do for normal virtual GRFs.

Signed-off-by: Lionel Landwerlin lionel.g.landwerlin@intel.com Cc: mesa-stable@lists.freedesktop.org