scsi: ufs: Tidy clocks list head usage

Move the initialization of clocks list head to ufshcd_alloc_host() so
that every driver doesn't have to do it. Remove checks for the list head
being NULL because that is not possible.

Signed-off-by: Szymon Mielczarek <szymonx.mielczarek@intel.com>
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Reviewed-by: Subhash Jadavani <subhashj@codeaurora.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>