scsi: ufs: fix static checker warning in ufshcd_populate_vreg

This patch fixes newly introduced static checker warning in
ufshcd_populate_vreg, introduced by UFS power management series.

Warning:
drivers/scsi/ufs/ufshcd-pltfrm.c:167 ufshcd_populate_vreg()
warn: missing error code here? 'devm_kzalloc()' failed. 'ret' = '0'

To fix it we return -ENOMEM and skip the message print.

Signed-off-by: Dolev Raviv <draviv@codeaurora.org>
Reviewed-by: Maya Erez <merez@codeaurora.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>