mesa: reset offset/size to 0 when removing atomic binding

mesa: reset offset/size to 0 when removing atomic binding

Similar to commit dd9d2963d6 (mesa: AtomicBufferBindings should be
initialized to zero.), we should reset these to zero when unbinding.
This fixes a number of dEQP failures due to cross-test pollution. The
tests properly unbound everything, but when querying the values again,
the expectation was that they would be 0.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Francisco Jerez <currojerez@riseup.net>