char: msm_smd_pkt: flush pending work on release

If an SMD device is closed while the device is active and then
immediately re-opened, then a delayed work item may get processed while
data structures are in the process of being re-initialized.

Move initialization of data structures to device creation which happens
once during module initialization.

CRs-Fixed: 698603
Change-Id: Ida85d8452f32b62fd848c706ba046f1a9a08bc85
Signed-off-by: Eric Holmberg <eholmber@codeaurora.org>