sha/asm/sha512p8-ppc.pl: fix build on Mac OS X.

Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6419)

crypto/sha/asm/sha512p8-ppc.pl

@@ -92,8 +92,7 @@ $idx="r7";
 $lrsave="r8";
 $offload="r11";
 $vrsave="r12";
-@I = ($x00,$x10,$x20,$x30,$x40,$x50,$x60,$x70)=map("r$_",(0,10,26..31));
-      $x00=0 if ($flavour =~ /osx/);
+@I = ($x00,$x10,$x20,$x30,$x40,$x50,$x60,$x70) = (0,map("r$_",(10,26..31)));
 
 @V=($A,$B,$C,$D,$E,$F,$G,$H)=map("v$_",(0..7));
 @X=map("v$_",(8..19,24..27));