drivers/fmc: The only way to dump the SDB is from debugfs

Driver should not call fmc_sdb_dump() anymore. (actually they can but the
operation is not supported, so it will print an error message)

Signed-off-by: Federico Vaga <federico.vaga@cern.ch>
Tested-by: Pat Riehecky <riehecky@fnal.gov>
Acked-by: Alessandro Rubini <rubini@gnudd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>