imx-drm: imx-tve: Provide __acquires/__releases annotation

Fix the following sparse warnings:

drivers/staging/imx-drm/imx-tve.c:133:13: warning: context imbalance in 'tve_lock' - wrong count at exit
drivers/staging/imx-drm/imx-tve.c:139:13: warning: context imbalance in 'tve_unlock' - unexpected unlock

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>