clk: ast2600: Fix enabling of clocks

The struct clk_ops enable callback for the aspeed gates mixes up the set
to clear and write to set registers.

Fixes: d3d04f6c ("clk: Add support for AST2600 SoC")
Reviewed-by: Andrew Jeffery <andrew@aj.id.au>
Signed-off-by: Joel Stanley <joel@jms.id.au>
Link: https://lkml.kernel.org/r/20191016131319.31318-1-joel@jms.id.au


Signed-off-by: Stephen Boyd <sboyd@kernel.org>