bn: Use a basic branch-if-not-zero

Ancient toolchains fail the build because they don't like the hints,
newer ISAs recommend not using the hints and relying on dynamic branch
prediction.

Signed-off-by: Martin Schwenke <martin@meltin.net>

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/15971)

crypto/bn/asm/ppc64-mont-fixed.pl

@@ -267,7 +267,7 @@ ___
 	addze		$tp[$n],$tp[$n+1]
 
 	addi		$i,$i,$SIZE_T
-	bc		25,0,$label->{"outer"}
+	bdnz		$label->{"outer"}
 
 	and.		$tp[$n],$tp[$n],$tp[$n]
 	bne		$label->{"sub"}