scsi: ufs: fix queue depth calculation for well-known logical unit

Some well-known logical unit may not support unit descriptor
and hence lun queue depth cannot be retrieved from the device.
Since these logical units are used only for special purpose,
a queue depth of one is set by default.

Change-Id: Ic41989789194a82eff74180b3ea7fd62c41d5b7b
Signed-off-by: Sujit Reddy Thumma <sthumma@codeaurora.org>
Signed-off-by: Dolev Raviv <draviv@codeaurora.org>