qcow2: Remove BDS parameter from qcow2_cache_get_table_idx()

qcow2: Remove BDS parameter from qcow2_cache_get_table_idx()

This function was only using the BlockDriverState parameter to get the
cache table size (since it was equal to the cluster size). This is no
longer necessary so this parameter can be removed.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-id: da3575d47c9a181a2cfd4715e53dd84a2c651017.1517840876.git.berto@igalia.com
Signed-off-by: Max Reitz <mreitz@redhat.com>