scsi: ufs: Avoid uninitialized use of offset

In function ufs_qcom_testbus_config, offset variable is
declared but not initialized. Switch case can take the
default case and use the uninitialized offset variable.
This change fixes the uninitialized use of offset.

Change-Id: I772296ef5606bc519dfcd00bfa6995b2d8646b9c
Signed-off-by: Sayali Lokhande <sayalil@codeaurora.org>