clk: sunxi-ng: explicitly include linux/spinlock.h

ccu_reset.h and ccu_reset.c use spinlock_t and associated functions but
rely on implict inclusion of linux/spinlock.h which means that changes
in other headers could break the build. Thus, add an explicit include.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>