clk: ast2600: allow empty entries in aspeed_g6_gates

We're about to remove an entry from aspeed_g6_gates, but we won't want
to alter/reorder existing entries. Allow empty entries in this array.

Reviewed-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Link: https://lore.kernel.org/r/20230302005834.13171-2-jk@codeconstruct.com.au


Tested-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>