Flash LED tps61310: use alloc_workqueue() instead of create_workqueue()

MSM8930 uses tps61310 in which work_queue was getting created
each time flash is turned ON. So using alloc_workqueue().

CRs-Fixed: 597864
Change-Id: I6e487cf4d17e66c22aed588f3ba55d32e41b21a2
Signed-off-by: Vijaya Kumar T M <vtmuni@codeaurora.org>