diag: Release wake source in case for write failure

There can be cases where writes to USB may fail. In that case
diag must release the wake source hold earlier. This patch
resolves the same.

Change-Id: I0f7d0312816a873a640a2b26fd5bed3ca80535f7
Signed-off-by: Katish Paran <kparan@codeaurora.org>