i965: Resolve GCC sign-compare warning.

i965: Resolve GCC sign-compare warning.

mesa/src/mesa/drivers/dri/i965/brw_vs_surface_state.c: In function 'brw_upload_pull_constants':
mesa/src/mesa/drivers/dri/i965/brw_vs_surface_state.c:84:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for (i = 0; i < prog_data->nr_pull_params; i++) {
                  ^
mesa/src/mesa/drivers/dri/i965/brw_vs_surface_state.c:89:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
       for (i = 0; i < ALIGN(prog_data->nr_pull_params, 4) / 4; i++) {
                     ^

Signed-off-by: Rhys Kidd <rhyskidd@gmail.com>
Reviewed-by: Thomas Helland <thomashelland90@gmail.com>