[Files.app] Fix the permissions of the icon files

I've added icon files for audio player at r247591, but their permissions are 755 and it is wrong. This patch fix them to 644.

TBR=yoshiki@chromium.org
BUG=none
TEST=none

Review URL: https://codereview.chromium.org/130803007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247608 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247608