nv50,nvc0: fix blit 3d path for 1d array textures

Need to adjust coordinates since the shader receives the array index as
depth in z, but the TEX instruction expects it to be the second
coordinate for a 1D array texture. This fixes fbo-generatemipmap-array.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Cc: "10.2" <mesa-stable@lists.freedesktop.org>