Mostly revert r521.

It was obviously an April joke: iErrorCode which was renamed iPICCError is
indeed a PCD Error, so I renamed it to iLastError since communications errors are
also to handle at the device driver level (read chip level), although I guess
that some errors would be common to distinct devices.
PICC error are irrelevant because they can either be transmission error
detection (in which case the libnfc should retry the transmission) or
application-level errors the libnfc cannot be aware of.

include/nfc/nfc-types.h

@@ -69,8 +69,8 @@ typedef struct {
   bool bPar;
 /** The last tx bits setting, we need to reset this if it does not apply anymore */
   uint8_t ui8TxBits;
-/** Last error reported by the PICC */
-  int iPICCError;
+/** Last error reported by the PCD / encountered by the PCD driver */
+  int iLastError;
 } nfc_device_t;