testsuite: arm: Fix build error for thumb2-slow-flash-data-3.c test

gcc/testsuite/ChangeLog:

	* gcc.target/arm/thumb2-slow-flash-data-3.c: Added argument to
	fn1 to avoid compile error.

Signed-off-by: Torbjörn SVENSSON <[email protected]>
(cherry picked from commit 09499ff)

Author: Torbjorn-Svensson

gcc/testsuite/gcc.target/arm/thumb2-slow-flash-data-3.c

@@ -10,7 +10,7 @@
 /* From PR71607 */
 
 float b;
-void fn1 ();
+void fn1 (void*);
 
 float
 fn2 ()