clk: agilex/stratix10/n5x: fix how the bypass_reg is handled

If the bypass_reg is set, then we can return the bypass parent, however,
if there is not a bypass_reg, we need to figure what the correct parent
mux is.

The previous code never handled the parent mux if there was a
bypass_reg.

Fixes: 80c6b7a0

 ("clk: socfpga: agilex: add clock driver for the Agilex platform")
Cc: stable@vger.kernel.org
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>
Link: https://lore.kernel.org/r/20210611025201.118799-4-dinguyen@kernel.org
Signed-off-by: Stephen Boyd <sboyd@kernel.org>