llvmpipe: fix using non-zero layer in non-array view from array resource

llvmpipe: fix using non-zero layer in non-array view from array resource

Just need to use resource target not view target when calculating
first-layer based mip offsets. (This is a gl specific problem since
d3d10 does not distinguish between non-array and array resources neither
at the resource nor view level, only at the shader level.)
Fixes new piglit arb_texture_view sampling-2d-array-as-2d-layer test.

Reviewed-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Jose Fonseca <jfonseca@vmware.com>