i965: Don't flush the batch at the end of blorp.

i965: Don't flush the batch at the end of blorp.

Improves GLB2.7 performance 0.13% +/- 0.09% (n=104/105, outliers removed).
More importantly, once color glClear()s are done through blorp in the next
commit, this reduces regression in GLES3 conformance tests that rely on
queueing up many glClear()s and having the GPU report being still busy in
an ARB_sync query after that.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>