Due to development history FreeBSD driver error codes are reported the same way
as in Linux (as negatives) which is inconsistent with FreeBSD standard. It may
cause unexpected behavior when driver errors are interpreted by a kernel
as syscall handler return values.
This patch converts error codes from negative to positive values for
NVM access functions.
Signed-off-by: Pawel Sobczyk <pawel.sobczyk@intel.com>