mmc: msm_sdcc: don't return error if regulator info is not available

On some platforms, few SDCC slots may be powered by always-on regulators
on board and in this case, regulator info for such SDCC slot is not
defined as part of their platform data. So let's not return error from
driver if regulator info is not present for a SDCC slot.

Change-Id: I902a322538d7400b5ce7fc33b1cf90a9cc4d6bfd
Signed-off-by: Asutosh Das <asutoshd@codeaurora.org>
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>