nfc: nci: Add comment to explain NCI_HCI_MAX_PIPES

According to specification etsi 102 622 chapter 4.4 pipes
identifier is 7 bits long giving a 127 possible pipes value.
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NChristophe Ricard <christophe-h.ricard@st.com>
Signed-off-by: NSamuel Ortiz <sameo@linux.intel.com>

include/net/nfc/nci_core.h

@@ -138,6 +138,10 @@ struct nci_conn_info {
 #define NCI_HCI_INVALID_HOST               0x80
 
 #define NCI_HCI_MAX_CUSTOM_GATES   50
+/*
+ * According to specification 102 622 chapter 4.4 Pipes,
+ * the pipe identifier is 7 bits long.
+ */
 #define NCI_HCI_MAX_PIPES          127
 
 struct nci_hci_gate {