package/sdl_sound: fix build with physfs

package/sdl_sound: fix build with physfs

A buildroot package for physfs has recently been added, and if it is
detected by sdl_sound's configure it enables code in the simple
player which fails to build (if the player is enabled).

(The build problem is due to physfs renaming a macro which has not been
reflected in sdl_sound.)

So, add the physfs dependency to the package information and correct
the build problem with a patch taken from Arch Linux, where they seem
to have already found and fixed this issue.

Fixes:
http://autobuild.buildroot.net/results/ae5839b978244c434dd86d49b672c437a7b19a66

Signed-off-by: Sam Bobroff <sam.bobroff@au1.ibm.com>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>