netlib_xarp: remove redundant cast

removes redundant type casts in ARP-related network library functions.
The casts from req.arp_dev (already a char array) to (FAR char *)
are unnecessary and can be safely removed.

Signed-off-by: zhanghongyu <zhanghongyu@xiaomi.com>

nshlib/nsh_netcmds.c

@@ -1310,7 +1310,7 @@ int cmd_arp(FAR struct nsh_vtbl_s *vtbl, int argc, FAR char **argv)
           FAR uint8_t *ptr;
 
           if (ifname != NULL &&
-              strcmp(ifname, (FAR char *)arptab[i].arp_dev) != 0)
+              strcmp(ifname, arptab[i].arp_dev) != 0)
             {
               continue;
             }