drm/mcde: Do not needlessly logically and with 3

The i index i always 0..3 in these statements so there
is no need to tag "& 3" to clamp it to 3 here. Make
the operator precedence explicit even if it's correct
as it is, the paranthesis creates less cognitive stress
for humans.

Reviewed-by: Stephan Gerhold <stephan@gerhold.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191122072508.25677-1-linus.walleij@linaro.org