clk: ast2600: BCLK comes from EPLL

clk: ast2600: BCLK comes from EPLL

This correction was made in the u-boot SDK recently. There are no
in-tree users of this clock so the impact is minimal.

Fixes: d3d04f6c330a ("clk: Add support for AST2600 SoC")
Link: https://github.com/AspeedTech-BMC/u-boot/commit/8ad54a5ae15f27fea5e894cc2539a20d90019717
Signed-off-by: Joel Stanley <joel@jms.id.au>
Link: https://lore.kernel.org/r/20220421040426.171256-1-joel@jms.id.au
Signed-off-by: Stephen Boyd <sboyd@kernel.org>