drm: omapdrm: dsi: Make wait_for_bit_change() return a status

The wait_for_bit_change() function returns the value of the bit it
polls. This requires the caller to compare the return value to the
expected bit value. As all the existing callers need is to check whether
the bit has reached the expected value, it's easier to return a boolean
status from the function.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>