[WESTON][i.MX] fix crash on monitor hotplug (or unplug)

In case of streaming data to the video outputs through playing a video or similar, weston crashed on i.MX SoCs on HDMI hotplug (or unplug). This happened because of incorrect handling of atomic operations failing to update the KMS (kernel mode setting) state, as seen through the following log messages:

atomic: couldn't commit new state: Device or resource busy applying repaint-start state failed: No such file or directory