msm: smd_pkt: Fix wakelock concurrency issue

In failure conditions, some clients violate the SMD PKT restriction of
single-threaded access resulting in overlapping open requests which
corrupt the wakelock list.

Move the wakelock initialization into the channel mutex to prevent
concurrent access from corrupting the wakelock.

CRs-Fixed: 374644
Change-Id: Idfdfc07fa69258d29154c4fce3fbcf2f000e63d6
Signed-off-by: Eric Holmberg <eholmber@codeaurora.org>