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/entry/vdso/vdso2c.c

@@ -65,6 +65,7 @@
 
 #include <linux/elf.h>
 #include <linux/types.h>
+#include <linux/kernel.h>
 
 const char *outfilename;
 
@@ -151,7 +152,7 @@ extern void bad_put_le(void);
 	PLE(x, val, 64, PLE(x, val, 32, PLE(x, val, 16, LAST_PLE(x, val))))
 
 
-#define NSYMS (sizeof(required_syms) / sizeof(required_syms[0]))
+#define NSYMS ARRAY_SIZE(required_syms)
 
 #define BITSFUNC3(name, bits, suffix) name##bits##suffix
 #define BITSFUNC2(name, bits, suffix) BITSFUNC3(name, bits, suffix)