package/ffmpeg: security bump to version 3.3.4

Fixes a number of integer overflows and DoS issues.

[Peter: explain security impact]
Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/ffmpeg/ffmpeg.hash

@@ -1,2 +1,2 @@
 # Locally calculated
-sha256 d2a9002cdc6b533b59728827186c044ad02ba64841f1b7cd6c21779875453a1e  ffmpeg-3.3.3.tar.xz
+sha256 98b97e1b908dfeb6aeb6d407e5a5eacdfc253a40c2d195f5867ed2d1d46ea957  ffmpeg-3.3.4.tar.xz

package/ffmpeg/ffmpeg.mk

@@ -4,7 +4,7 @@
 #
 ################################################################################
 
-FFMPEG_VERSION = 3.3.3
+FFMPEG_VERSION = 3.3.4
 FFMPEG_SOURCE = ffmpeg-$(FFMPEG_VERSION).tar.xz
 FFMPEG_SITE = http://ffmpeg.org/releases
 FFMPEG_INSTALL_STAGING = YES