mx53loco: Remove unneeded 'retval' variable

commit c7336815 (pmic: Extend PMIC framework to support multiple instances
of PMIC devices) introduced an extra 'retval' variable, but this is not
necessary since we have already the variable 'ret' in place.

So use 'ret' to store the return values from the pmic related calls and remove
'retval'.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>