contrib: use ffmpeg v4.2.2 for apple devices

On iOS ffmpeg v4.3 causes crash when using vp8 codec.

Change-Id: Iae93f66979b81d2abf6dbc2a653142538b69d009

contrib/src/ffmpeg/SHA512SUMS

-ifdef HAVE_MACOSX
+ifdef HAVE_DARWIN_OS
 df0393b9dbee05f64f80ff98512ec153c78ccca9f8ea170301703cd0b92fb68c91c8113ab8a2ecb161ac465544edefe29dd1965e6959694f8728fee529606665  ffmpeg-n4.2.2.tar.gz
 else
 b00ca3b77e9c9a4ee69a50283471bf136c1a35a837982aa886e9c50c546e48a6b5ea2acd1e183990eefe6c32fb1d5504684925abb7d8fa4f80b7e53864647c6c  ffmpeg-n4.3.tar.gz

contrib/src/ffmpeg/rules.mak

-ifdef HAVE_MACOSX
+ifdef HAVE_DARWIN_OS
 FFMPEG_HASH := n4.2.2
 else
 FFMPEG_HASH := n4.3