drm/gma500: use ARRAY_SIZE

drm/gma500: use ARRAY_SIZE

Using the ARRAY_SIZE macro improves the readability of the code. Also,
it is useless to re-invent it.

Found with Coccinelle with the following semantic patch:
@r depends on (org || report)@
type T;
T[] E;
position p;
@@
(
 (sizeof(E)@p /sizeof(*E))
|
 (sizeof(E)@p /sizeof(E[...]))
|
 (sizeof(E)@p /sizeof(T))
)

Reviewed-by: Thierry Reding <[email protected]>
Signed-off-by: Jérémy Lefaure <[email protected]>
Signed-off-by: Daniel Vetter <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]