STM32MP1: Fix unable to reconnect device issue

Sometimes, the system wouldn't able to reconnect to the device
while flashing the firmware [1]
This issue was happened on the health-check job [2].
We'll take the same approach to resolve it [3]

[1]: https://tf.validation.linaro.org/scheduler/job/1979463#L238
[2]: https://linaro.atlassian.net/browse/TFC-469
[3]: https://linaro.atlassian.net/browse/TFC-469?focusedCommentId=202082

Signed-off-by: Arthur She <arthur.she@linaro.org>
Change-Id: I7827c50d0ccf83bd0c1fa109bd605d27b9ce3171
1 file changed