msm: mhi: initialize variables to default values

Few functions have variables which might get used with out
proper initialization. Initialize variables to default values.

CRs-Fixed: 2087109
Change-Id: I7645940e8d466e0ef67a5b8b7702b18b160cc10f
Signed-off-by: Rama Krishna Phani A <rphani@codeaurora.org>