scsi: ufs: Initialize cmd_id and check lrbp->cmd NULL

In commit d70b0a18 ("scsi: ufs: add command
logging infrastructure"), cmd_id is not initialized
and lrbp->cmd is explicitly dereferenced without
checking NULL. Fix them by initializing cmd_id with
an initial value 0 and checking NULL for lrbp->cmd.

Change-Id: I6f66066adc8d53e3615df50ac49dd313f6d7ea8e
Signed-off-by: Can Guo <cang@codeaurora.org>