sysctl.c: use strchr() instead of index()

index() is a legacy function, which is no longer implemented by all C
libraries (example: uClibc). Instead, use the POSIX defined strchr()
function.

Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

sysctl.c

@@ -814,7 +814,7 @@ int main(int argc, char *argv[])
 		      program_invocation_short_name);
 
 	for ( ; *argv; argv++) {
-		if (WriteMode || index(*argv, '='))
+		if (WriteMode || strchr(*argv, '='))
 			ReturnCode += WriteSetting(*argv);
 		else
 			ReturnCode += ReadSetting(*argv);