i965: Preserve EXEC_OBJECT_CAPTURE when growing the BO.

i965: Preserve EXEC_OBJECT_CAPTURE when growing the BO.

The original state buffer was marked with EXEC_OBJECT_CAPTURE.  When
growing it, we want to preserve that flag so we continue to capture it
in GPU hang reports.

Fixes: 2dfc119f22f257082ab0 "i965: Grow the batch/state buffers if we need space and can't flush."
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>