package/gerbera: fix build with latest exiv2

package/gerbera: fix build with latest exiv2

After the bump to exiv2 0.27.1 a build error due to missing header
inclusion appeared.

Fixes:
http://autobuild.buildroot.net/results/3831acf7f4c5a9f1a404e0ced3d6bec7a2249601/
http://autobuild.buildroot.net/results/de0545462c6017fe54acc284b914b9fa8b0172d8/

The patch is waiting merge into the mainline
https://github.com/gerbera/gerbera/pull/457

Signed-off-by: Nicolas Serafini <nicolas.serafini@sensefly.com>
[Arnout: include as a patch instead of downloading it, due to hash]
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>