multimedia/libvpx: backport VP9 fix (direct commit)

Obtained from:	upstream (libvpx 1.7.0, via Firefox 59)
Approved by:	ports-secteam blanket

multimedia/libvpx/Makefile

@@ -4,7 +4,7 @@
 PORTNAME=	libvpx
 DISTVERSIONPREFIX=	v
 DISTVERSION=	1.6.1
-PORTREVISION=	3
+PORTREVISION=	4
 CATEGORIES=	multimedia
 
 PATCH_SITES=	https://github.com/${GH_ACCOUNT}/${GH_PROJECT}/commit/

multimedia/libvpx/files/patch-mozilla-bug1443865

@@ -0,0 +1,13 @@
+https://chromium.googlesource.com/webm/libvpx/+/84a7263d4c12%5E!/
+
+--- vp9/encoder/x86/vp9_quantize_ssse3_x86_64.asm.orig	2017-01-12 20:27:27 UTC
++++ vp9/encoder/x86/vp9_quantize_ssse3_x86_64.asm
+@@ -171,7 +171,7 @@ cglobal quantize_%1, 0, %2, 15, coeff, ncoeff, skip, z
+   pshuflw                         m7, m8, 0x1
+   pmaxsw                          m8, m7
+   pextrw                          r6, m8, 0
+-  mov                           [r2], r6
++  mov                           [r2], r6w
+   RET
+ 
+   ; skip-block, i.e. just write all zeroes