serial: stm32: move dma_request_chan() before clk_prepare_enable()

If dma_request_chan() returns a PROBE_DEFER error, clk_disable_unprepare()
will be called and USART clock will be disabled. But early console can be
still active on the same USART.

While moving dma_request_chan() before clk_prepare_enable(), the clock
won't be taken in case of a DMA PROBE_DEFER error, and so it doesn't need
to be disabled. Then USART is still clocked for early console.

Fixes: a7770a4b ("serial: stm32: defer probe for dma devices")
Reported-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Valentin Caron <valentin.caron@foss.st.com>
Link: https://lore.kernel.org/r/20221118170602.1057863-1-valentin.caron@foss.st.com


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