scsi: ufs: fix an error in getting UFS spec version

The UFS spec version should be read out from the buffer which stores device
descriptor before the buffer is cleared and used for reading other
descriptors. Otherwise we will get wrong values.

Change-Id: I56e665c010ceaf0916313a74926ce442874f824f
Signed-off-by: Can Guo <cang@codeaurora.org>