package/sdl_ttf: bump to de50cffd41e6

package/sdl_ttf: bump to de50cffd41e6

There is unlikely to be a new SDL_ttf release for the foreseeable future:
https://bugzilla.libsdl.org/show_bug.cgi?id=5344#c1

The unreleased version from HEAD as of 2020-11-09 has several bugfixes
and DPI scaling support:
https://hg.libsdl.org/SDL_ttf/rev/7dbd7cd826d6

DPI scaling is used for rendering on HiDPI displays and displays
with non-square pixels.

Signed-off-by: Gleb Mazovetskiy <glex.spb@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>