i965: Resolve GCC sign-compare warning.

i965: Resolve GCC sign-compare warning.

mesa/src/mesa/drivers/dri/i965/intel_screen.c: In function 'intel_screen_make_configs':
mesa/src/mesa/drivers/dri/i965/intel_screen.c:1222:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for (int i = 0; i < ARRAY_SIZE(formats); i++) {
                      ^
mesa/src/mesa/drivers/dri/i965/intel_screen.c:1259:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for (int i = 0; i < ARRAY_SIZE(formats); i++) {
                      ^
mesa/src/mesa/drivers/dri/i965/intel_screen.c:1291:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for (int i = 0; i < ARRAY_SIZE(formats); i++) {
                      ^

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