staging: media: atomisp: add missing include in vlv2_plat_clock.c

To use IO functions like writel, readl, ioremap_nocache and iounmap,
linux/io.h should be included.

Signed-off-by: Jérémy Lefaure <jeremy.lefaure@lse.epita.fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>