configure.ac: s/xcb-fixes/xcb-xfixes/

Former is not a thing, even if I have a hacked xcb-fixes.pc on my system.
Thanks for spotting it Mark!

Fixes: 9a90d6a9d4e ("configure.ac: add xcb-fixes to the XCB DRI3 list")
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
1 file changed