ion: msm: Correct msm_ion_parse_dt() error propagation

If a device cannot be created for a child node, or the ID cannot
be retrieved for a heap, then msm_ion_parse_dt() will return ret.
However, under these circumstances, ret has not been updated to
reflect these failures, and as such, msm_ion_probe will erroneously
continue as if the call to msm_ion_parse_dt() had been successful.
Thus, ensure that ret is set before following the error path in
msm_ion_parse_dt().

Change-Id: I241805e2c169fb15bda68c2a375def04790aa20e
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>