wpa_supplicant: fix errors for GCC 8 support
wpa_supplicant: fix errors for GCC 8 support

components/wpa_supplicant/port/include/os.h:259:29: error: 'strncpy' output truncated before terminating nul copying 3 bytes from a string of the same length [-Werror=stringop-truncation]
 #define os_strncpy(d, s, n) strncpy((d), (s), (n))
                             ^~~~~~~~~~~~~~~~~~~~~~
components/wpa_supplicant/src/wpa2/eap_peer/eap.c:410:3: note: in expansion of macro 'os_strncpy'
   os_strncpy(sm->blob[0].name, CLIENT_CERT_NAME, BLOB_NAME_LEN);
   ^~~~~~~~~~

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