install-ffmpeg-ios.sh: use a proper dylib regexp

To fix only names of FFmpeg frameworks, not system libraries/dylibs.

Pick-to: 6.9.0 6.8
Fixes: QTBUG-134289
Change-Id: I74ef7700549abdccbe569ecd5d8e780fefca6e11
Reviewed-by: Jani Heikkinen <jani.heikkinen@qt.io>
Reviewed-by: Jøger Hansegård <joger.hansegard@qt.io>

Author: Timur Pocheptsov

coin/provisioning/common/unix/install-ffmpeg-ios.sh

@@ -19,6 +19,7 @@ ffmpeg_name="FFmpeg-$version"
 target_dir="$HOME"
 ffmpeg_source_dir="$target_dir/$ffmpeg_name"
 prefix="/usr/local/ios/ffmpeg"
+dylib_regex="^@rpath/.*\.dylib$"
 
 if [ ! -d "$ffmpeg_source_dir" ];
 then