i965: Don't use brw->fragment_program in the old brw_wm_pass2.c.

i965: Don't use brw->fragment_program in the old brw_wm_pass2.c.

According to Eric, this shouldn't matter since we don't do precompiles
using the old backend.  In other words, brw->fragment_program (the
currently active program) should equal c->fp (the program currently
being compiled).

However, it's just not a good idea to access brw->fragment_program
directly in compiler code.  It's totally illegal in the new backend, so
let's just not do it here either.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reported-by: Paul Berry <stereotype441@gmail.com>