video: pxa3xx-gcu: Simplify the logic to exit while loop in pxa3xx_gcu_wait_idle

If wait_event_interruptible_timeout returns a positive value, it means
the condition evaluated is true. Which means priv->shared->hw_running is false.
And then we will exit the loop.

This patch simplifies the logic to exit the while loop.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>