mhi: controller: Enable L1 when mhi is not active

offload worker checks if mhi is active before doing the reg
write. If mhi is not active it returns without enabling L1.
This causes prevent_l1 counter to go out of sync. Fix this
by enabling L1 before returning from offload worker function.

Change-Id: I8a356acca3d8b8a7b4ff4d95e7378a056a2b06cf
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>