st/mesa: fix levels in initial texture creation

calim pointed out we were getting mipmap levels for array multisamples,
this didn't make sense. So then I noticed this function takes last_level
so we are passing in a too high value here.

I think this should fix the case he was seeing.

Reviewed-by: Brian Paul <brianp@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

src/mesa/state_tracker/st_cb_texture.c

@@ -1662,7 +1662,7 @@ st_AllocTextureStorage(struct gl_context *ctx,
    stObj->pt = st_texture_create(st,
                                  gl_target_to_pipe(texObj->Target),
                                  fmt,
-                                 levels,
+                                 levels - 1,
                                  ptWidth,
                                  ptHeight,
                                  ptDepth,