Fix various problems in I2C support of PN532: - Fix a memory leak in pn532_i2c_wait_rdyframe() - Remove unused parameters and local variables - Fix all other compilation warnings

Note: a new constant (PN53x_ACK_FRAME__LEN) has been defined in
pn53x-internal.h file to avoid hard coding the ACK frame length.

libnfc/chips/pn53x-internal.h

@@ -116,6 +116,7 @@
 #  define PN53x_NORMAL_FRAME__OVERHEAD			8
 #  define PN53x_EXTENDED_FRAME__DATA_MAX_LEN		264
 #  define PN53x_EXTENDED_FRAME__OVERHEAD		11
+#  define PN53x_ACK_FRAME__LEN                          6
 
 typedef struct {
   uint8_t ui8Code;