scsi: ufs: Add back a missing sanity check to ufshcd_read_desc_param()

Commit a78751da13c9e
("scsi: ufs: Fix unexpected values get from ufshcd_read_desc_param()")
wrongly deletes a condition check for tmp buffer allocation, this change
adds it back.

Change-Id: I0f27f30c90fd6592e10af039ce8227d48a85c790
Signed-off-by: Can Guo <cang@codeaurora.org>