phy: qcom-ufs: Remove unnecessary BUG_ON

BUG_ON() are not preferred in the driver, plus the variable
on which BUG_ON is asserted is already checked in the code
before passing.

Signed-off-by: Vivek Gautam <vivek.gautam@codeaurora.org>
Reviewed-by: Subhash Jadavani <subhashj@codeaurora.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>