crypto/aes: minor ppc64 assembly naming improvements

doEncryptKeyAsm is tail-called from other assembly routines.
Give it a proper prototype so that vet can check it.
Adjust one assembly FP reference accordingly.

Change-Id: I263fcb0191529214b16e6bd67330fadee492eef4
Reviewed-on: https://go-review.googlesource.com/37305
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/crypto/aes/asm_ppc64le.s

@@ -439,7 +439,7 @@ TEXT ·decryptBlockAsm(SB),NOSPLIT|NOFRAME,$0
 	// Load the arguments inside the registers
 	MOVD dst+0(FP), BLK_OUT
 	MOVD src+8(FP), BLK_INP
-	MOVD enc+16(FP), BLK_KEY
+	MOVD dec+16(FP), BLK_KEY
 
 	MOVWZ 240(BLK_KEY), BLK_ROUNDS // lwz 6,240(5)
 	MOVD $15, BLK_IDX              // li 7,15

src/crypto/aes/cipher_ppc64le.go

@@ -20,7 +20,7 @@ func setDecryptKeyAsm(key *byte, keylen int, dec *uint32) int
 
 //go:noescape
 
-func doEncryptKeyAsm()
+func doEncryptKeyAsm(key *byte, keylen int, dec *uint32) int
 
 //go:noescape