IB/hfi1: Handle missing magic values in config file

Driver does not check whether proper configuration file exist in EPROM,
and treats empty partition as possible valid configuration, preventing
fallback to default firmware. Change EPROM read function to treat
missing magic number as read error.

Reviewed-by: Jakub Byczkowski <jakub.byczkowski@intel.com>
Signed-off-by: Jan Sokolowski <jan.sokolowski@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>