clk/ast2600: Fix soc revision for AHB

Move the soc revision parsing to the initial probe, saving the driver
from parsing the register multiple times.

Use this variable to select the correct divisor table for the AHB clock.
Before this fix the A2 would have used the A0 table.

Fixes: 2d491066 ("clk: ast2600: Fix AHB clock divider for A1")
Signed-off-by: Joel Stanley <joel@jms.id.au>
Link: https://lore.kernel.org/r/20210922235449.213631-1-joel@jms.id.au


Reviewed-by: Andrew Jeffery <andrew@aj.id.au>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>