i965: fix compiler error in union initiliazer

i965: fix compiler error in union initiliazer

gcc 4.6.3 chokes with the following error:

brw_vec4.cpp: In member function 'int brw::vec4_visitor::setup_uniforms(int)':
brw_vec4.cpp:1496:37: error: expected primary-expression before '.' token

Apparently C++ does not do named initializers for unions, except maybe
as a gcc extension, which is not present here.

As .f is the first element of the union, just drop it. Fixes the build
error.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Matt Turner <mattst88@gmail.com>