st/mesa: also move yoffset to zoffset for 1d array textures

Do the same as in st_TexSubImage. This fixes
arb_get_texture_sub_image-get on llvmpipe when it is set to prefer
blits, and nouveau when it uses the 3d engine for blits.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>

src/mesa/state_tracker/st_cb_texture.c

@@ -1071,6 +1071,8 @@ st_GetTexSubImage(struct gl_context * ctx,
 
    /* From now on, we need the gallium representation of dimensions. */
    if (gl_target == GL_TEXTURE_1D_ARRAY) {
+      zoffset = yoffset;
+      yoffset = 0;
       depth = height;
       height = 1;
    }