iommu/arm-smmu: Don't ignore clock/regulator API errors

The clock and regulator APIs can fail, but we're ignoring their return
values.  This results in strange code paths where we misuse the
API (e.g. we enable clocks after a failed prepare, which makes the clock
driver yell).  Fix this by checking all return values and propagating
the errors up to clients as needed.

CRs-Fixed: 924600
Change-Id: Ib6cb3afac1f5472f3a5abb5c251765344fe1a7a9
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>