serial: cpm_uart: Use get_baudrate() instead of uart_baudrate()

uart_baudrate() is just a trivial wrapper to get_baudrate().

Use get_baudrate() directly and remove assignment in if condition.

And also remove uart_clock() which is not used since
commit 0b2a2e5b ("cpm_uart: Remove !CONFIG_PPC_CPM_NEW_BINDING
code")

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Link: https://lore.kernel.org/r/4d497386f576a3df768e44a04f9bb512e424c311.1691068700.git.christophe.leroy@csgroup.eu


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>