mlxsw: spectrum_acl: Fix mlxsw_sp_acl_tcam_group_add()'s error path

If mlxsw_sp_acl_tcam_group_id_get() fails, the mutex initialized earlier
is not destroyed.

Fix this by initializing the mutex after calling the function. This is
symmetric to mlxsw_sp_acl_tcam_group_del().

Fixes: 5ec2ee28

 ("mlxsw: spectrum_acl: Introduce a mutex to guard region list updates")
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>