vulkan: Fix descriptor set creation with zero bindings.

vulkan: Fix descriptor set creation with zero bindings.

MAX2(count * struct size, 1) results in 1 for count=0, not the size of a struct.

Since this MAX only seems to exist so we can keep using NULL for error reporting,
just refactor to return a VkResult.

Fixes: ad241b15a9e ("vk: consolidate dynamic descriptor binding sorting")
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/4522
Reviewed-By: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Acked-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9880>