s390: remove indirect branch from do_softirq_own_stack

The inline assembly to call __do_softirq on the irq stack uses
an indirect branch. This can be replaced with a normal relative
branch.

Cc: stable@vger.kernel.org # 4.16
Fixes: f19fbd5 ("s390: introduce execute-trampolines for branches")
Reviewed-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

Author: Martin Schwidefsky

arch/s390/kernel/irq.c

@@ -176,10 +176,9 @@ void do_softirq_own_stack(void)
 		new -= STACK_FRAME_OVERHEAD;
 		((struct stack_frame *) new)->back_chain = old;
 		asm volatile("   la    15,0(%0)\n"
-			     "   basr  14,%2\n"
+			     "   brasl 14,__do_softirq\n"
 			     "   la    15,0(%1)\n"
-			     : : "a" (new), "a" (old),
-			         "a" (__do_softirq)
+			     : : "a" (new), "a" (old)
 			     : "0", "1", "2", "3", "4", "5", "14",
 			       "cc", "memory" );
 	} else {