tftp: drop "inline" from definition of usage()

It is pointless and newer gcc say it is a lose.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
diff --git a/tftp/main.c b/tftp/main.c
index 1b8a881..b2f9059 100644
--- a/tftp/main.c
+++ b/tftp/main.c
@@ -188,7 +188,7 @@
 
 const char *program;
 
-static inline void usage(int errcode)
+static void usage(int errcode)
 {
     fprintf(stderr,
 #ifdef HAVE_IPV6