i965: Set miptree target field when creating from a BO.

i965: Set miptree target field when creating from a BO.

Prior to commit 8435b60a3577d2d905eae189cd7e770500177e99, the region
equivalent of this function called intel_miptree_create_layout, which
set mt->target to target.  With that commit, it no longer copied target.

Piglit's ext_image_dma_buf_import-sample_[xa]rgb8888 tests would then
hit an assertion failure, where image->TexObject->Target was
GL_TEXTURE_EXTERNAL_OES, and mt->target was GL_TEXTURE_2D.

Copying the target fixes this assertion failure.

Cc: "10.2" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>