uart: Read clock frequency from bus

[mkoz_semihalf.com]

Summary

It is stored in clock-frequency.
In case of failure, fallback to the harcoded value stored in the compat data.
While here improve style.
Tested on LS1046ARDB and x86 PC.

[mw]

sys/dev/uart/uart_bus_acpi.c

88

Don't assign value in declaration block.

95

missing space after return.

[mkoz_semihalf.com]

This comment was removed by mkoz_semihalf.com.

[mkoz_semihalf.com]

This comment was removed by mkoz_semihalf.com.

[mkoz_semihalf.com]

Move assignment.
Fix style in return statement.

[mkoz_semihalf.com]

Remove empty line.