The target parameter to _mesa_get_tex_image() is a target enum, not an index.
When we're setting up faces for a cubemap, it should be
CUBE_MAP_POSITIVE_X .. CUBE_MAP_NEGATIVE_Z; for all other targets it
should be the same as the texobj's target.

Fixes broken cubemaps [had only +X face but claimed to have all] produced by
glTextureView, which then caused various crashes in the driver when we
tried to use them.

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
Reviewed-by: Brian Paul <brianp@vmware.com>