crypto: caam - fix ERA property reading

In order to ensure that the ERA property is properly read from DT
on all platforms, of_property_read* function needs to be used.

Signed-off-by: Alex Porosanu <alexandru.porosanu@freescale.com>
Signed-off-by: Horia Geant? <horia.geanta@freescale.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>