blake2s: fix frame size of hashBlocksSSE4

The frame is actually 16 bytes plus alignment, not 0.

This fixes the build on Go 1.6.

Change-Id: Id3dcf4e1628791ed55a38a819dcf3c11ecc2f488
Reviewed-on: https://go-review.googlesource.com/31711
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

blake2s/blake2s_amd64.s

@@ -433,7 +433,7 @@ TEXT ·hashBlocksSSSE3(SB), 0, $672-48 // frame = 656 + 16 byte alignment
 	RET
 
 // func hashBlocksSSE4(h *[8]uint32, c *[2]uint32, flag uint32, blocks []byte)
-TEXT ·hashBlocksSSE4(SB), 0, $16-48 // frame = 0 + 16 byte alignment
+TEXT ·hashBlocksSSE4(SB), 0, $32-48 // frame = 16 + 16 byte alignment
 	HASH_BLOCKS(h+0(FP), c+8(FP), flag+16(FP), blocks_base+24(FP), blocks_len+32(FP), BLAKE2s_SSE4)
 	RET