powerpc/nvdimm: Use HCALL error as the return value

This simplifies the error handling and also enable us to switch to
H_SCM_QUERY hcall in a later patch on H_OVERLAP error.

We also do some kernel print formatting fixup in this patch.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190903123452.28620-1-aneesh.kumar@linux.ibm.com