anv: fix vkUpdateDescriptorSets with inline uniform blocks

With inline uniform blocks descriptor, the meaning of descriptorCount
is a number of bytes to copy into the descriptor. Don't try to use
that size as an index into the descriptor table.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Fixes: 43f40dc7 ("anv: Implement VK_EXT_inline_uniform_block")
Gitlab: https://gitlab.freedesktop.org/mesa/mesa/issues/1195


Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
(cherry picked from commit 3f8f52b2)