sha/asm/sha512p8-ppc.pl: fix typo in prologue.

Reviewed-by: NTim Hudson <tjh@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7643)

(cherry picked from commit 79d7fb990cd28bbe2888ed8f9051ab54c9f986b0)

crypto/sha/asm/sha512p8-ppc.pl

@@ -166,8 +166,8 @@ $func:
 	addi		r11,r11,32
 	stvx		v30,r10,$sp
 	stvx		v31,r11,$sp
-	li		r11,-4096+255
-	stw		$vrsave,`$FRAME+6*$SIZE_T-4`($sp)	# save vrsave
+	li		r11,-4096+255		# 0xfffff0ff
+	stw		$vrsave,`$FRAME-6*$SIZE_T-4`($sp)	# save vrsave
 	li		$x10,0x10
 	$PUSH		r26,`$FRAME-6*$SIZE_T`($sp)
 	li		$x20,0x20