mx53loco: Fix PMIC name

commit c7336815 (pmic: Extend PMIC framework to support multiple instances
of PMIC devices) has incorrectly passed the PMIC name under the FSL PMIC case.

Fix that by passing "FSL_PMIC" as the parameter of pmic_get.

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