drm/i2c: tda998x: don't freeze the system at audio startup time

This patch prevents the system to be freezed at audio startup time,
replacing mdelay by msleep.

Tested-by: Russell King <rmk+kernel@arm.linux.org.uk>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>