gadgetd: examples: Extend ffs host example to handle errors.
gadgetd: examples: Extend ffs host example to handle errors.

Bulk transfer may fail each time it is scheduled
so return value should be chacked to avoid silent
live lock.

Change-Id: I577a4a487004cf99c9a8864530b871199abcd6a2
Signed-off-by: Krzysztof Opasiak <8064eda6f94b3817252b7d7649cf754592f63500@samsung.com>

gadgetd/gadgetd,gadgetd/gadgetd,gadgetd/gadgetd