draw/llvm: set draw->pt.user.planes field in draw_set_clip_state()

draw/llvm: set draw->pt.user.planes field in draw_set_clip_state()

Previously it was getting set in draw_set_mapped_constant_buffer() but
if there were no shader constants, that function wasn't called.  So the
pt.user.planes field was null and we died when we tried to access the
clip planes in the LLVM-generated code.

Fixes https://bugs.freedesktop.org/show_bug.cgi?id=41663

Note: This is a candidate for the 7.11 branch.

Reviewed-by: José Fonseca <jfonseca@vmware.com>