powerpc/book3s: Fix some ABIv2 issues in machine check code

Commit 2749a2f2 (powerpc/book3s: Fix machine check handling for
unhandled errors) introduced a few ABIv2 issues.

We can maintain ABIv1 and ABIv2 compatibility by branching to the
function rather than the dot symbol.

Fixes: 2749a2f2 ("powerpc/book3s: Fix machine check handling for unhandled errors")
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/exceptions-64s.S

@@ -1502,13 +1502,13 @@ machine_check_handle_early:
 unrecover_mce:
 	/* Invoke machine_check_exception to print MCE event and panic. */
 	addi	r3,r1,STACK_FRAME_OVERHEAD
-	bl	.machine_check_exception
+	bl	machine_check_exception
 	/*
 	 * We will not reach here. Even if we did, there is no way out. Call
 	 * unrecoverable_exception and die.
 	 */
 1:	addi	r3,r1,STACK_FRAME_OVERHEAD
-	bl	.unrecoverable_exception
+	bl	unrecoverable_exception
 	b	1b
 /*
  * r13 points to the PACA, r9 contains the saved CR,