slimbus: Avoid uninitialized variable access

Avoid reading uninitalized variables.
Initialize it to default value before reading.

Change-Id: Ic34dfec16357cbc4992912e883f21f014cf8a66c
Signed-off-by: Dilip Kota <dkota@codeaurora.org>
Signed-off-by: Shrey Vijay <shreyv@codeaurora.org>