mesa: Inherit texture view multi-sample information from the original texture images.

Found running "The Witness" in Wine. Without this patch, texture views created
on multi-sample textures would have a GL_TEXTURE_SAMPLES of 0. All things
considered such views actually work surprisingly well, but when combined with
(plain) multi-sample textures in a framebuffer object, the resulting FBO is
incomplete because the sample counts don't match.

CC: <mesa-stable@lists.freedesktop.org>
Signed-off-by: Henri Verbeet <hverbeet@gmail.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
(cherry picked from commit 0b73c86b)