Tell C compiler we don't care about return code of libssh2_init

The call of libssh2_init returns a return code, but nothing could be done
within the _libssh2_init_if_needed execution path.

Signed-off-by: Steven Dake <sdake@redhat.com>

src/global.c

@@ -74,5 +74,5 @@ void
 _libssh2_init_if_needed(void)
 {
     if (_libssh2_initialized == 0)
-        libssh2_init (0);
+        (void)libssh2_init (0);
 }