Staging: rtl8712: Use ARRAY_SIZE macro

ARRAY_SIZE is more concise to use when the size of an array is divided
by the size of its type

Changes made using Coccinelle-

@@
type T;
T[] E;
@@

- (sizeof(E)/sizeof(T))
+ ARRAY_SIZE(E)

Signed-off-by: Shraddha Barke <shraddha.6596@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>