freedreno: Clamp UBO uploads to the constlen decided by the shader.

freedreno: Clamp UBO uploads to the constlen decided by the shader.

If the NIR-level analysis decided to move UBO loads to the constant
file, but the backend decided not to load those constants, we could
upload past the end of constlen.  This is particularly relevant for
pre-a6xx, where we emit a different constlen between bin and render
variants.

(Fix by Rob, commit message by anholt)

Reviewed-by: Eric Anholt <eric@anholt.net>