ARM: dts: msm: replace pmcobalt with pm8998 for msmskunk

As regulator names have changed from pmcobalt to pm8998, this change
updates the same for UFS nodes on RUMI as well.

Change-Id: Id9c5449a883a5bf0e24b8f24939b85e46ad1eb30
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>