x86: Use ARRAY_SIZE

Using the ARRAY_SIZE macro improves the readability of the code.

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))
)

Signed-off-by: Jérémy Lefaure <jeremy.lefaure@lse.epita.fr>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-video@atrey.karlin.mff.cuni.cz
Cc: Martin Mares <mj@ucw.cz>
Cc: Andy Lutomirski <luto@amacapital.net>
Link: https://lkml.kernel.org/r/20171001193101.8898-13-jeremy.lefaure@lse.epita.fr

arch/x86/boot/video-vga.c

@@ -241,9 +241,9 @@ static int vga_probe(void)
 		vga_modes,
 	};
 	static int mode_count[] = {
-		sizeof(cga_modes)/sizeof(struct mode_info),
-		sizeof(ega_modes)/sizeof(struct mode_info),
-		sizeof(vga_modes)/sizeof(struct mode_info),
+		ARRAY_SIZE(cga_modes),
+		ARRAY_SIZE(ega_modes),
+		ARRAY_SIZE(vga_modes),
 	};
 
 	struct biosregs ireg, oreg;