package/weston: fix build with newer freerdp

Commit a63aad66 (package/freerdp: bump version to 2.0.0-rc2)
introduced a FreeRDP that has a different API, and this breaks
weston.

Backport a patch from upstream weston to fix the issue.

Fixes:
    http://autobuild.buildroot.org/results/c0b4f7c4cee2c11715ecc2ef0cfb42f80dbf81b0/



Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>