api: remove superfluous assignment

No need to assign a value to sig if the next statement using sig
is itself an assignment of a value to sig.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>

api/api.c

@@ -625,7 +625,7 @@ int syscall(int call, int *retval, ...)
 
 void api_init(void)
 {
-	struct api_signature *sig = NULL;
+	struct api_signature *sig;
 
 	/* TODO put this into linker set one day... */
 	calls_table[API_RSVD] = NULL;