[SCSI] libfc: rport debug messages were printing pointer values

Don't print large negative decimal numbers for frame pointers in
the debug messages from fc_rport_error().  Just print 0 if its a
frame pointer, and print the error numbers as positive.

Signed-off-by: Joe Eykholt <jeykholt@cisco.com>
Signed-off-by: Robert Love <robert.w.love@intel.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>