video: Add missing annotation for cyber2000fb_enable_ddc() and cyber2000fb_disable_ddc()

Sparse reports warnings at cyber2000fb_enable_ddc()
	and cyber2000fb_disable_ddc()

warning: context imbalance in cyber2000fb_enable_ddc()
	- wrong count at exit

warning: context imbalance in cyber2000fb_disable_ddc()
	- unexpected unlock

The root cause is the missing annotation at cyber2000fb_enable_ddc()
	and cyber2000fb_disable_ddc()

Add the missing __acquires(&cfb->reg_b0_lock) annotation
Add the missing __releases(&cfb->reg_b0_lock) annotation

Signed-off-by: Jules Irenge <jbi.octave@gmail.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200403160505.2832-3-jbi.octave@gmail.com