radv: Unify max_descriptor_set_size.

They were out of sync. Besides syncing, lets ensure they never diverge
again.

Fixes: 8d2654a4 "radv: Support VK_EXT_inline_uniform_block."
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
(cherry picked from commit 4cde0e04)