drivers: serial: stm32: Fixes uart_event_tx len calculation

Resetting the dma_tx.buffer_length after the dma_tx.counter
calculation, instead of before.
We need to reset the buffer_length when the transmission is finished,
but in order to give the correct value to the uart_event_tx struct,
we use the dma_tx.buffer_length in the calculation of the
dma_tx.counter, used for the len of the event (number of bytes sent).
I found this problem, when I wanted to use the uart_event_tx.len for
freeing the used space inside a ring buffer (ring_buf_get_finish),
and it didn't work, I logged the values of the uart_event_tx struct,
and found out it always was 0, because the buffer_length was 0,
and the whole buffer was transmitted (stat.pending_length also 0).

Signed-off-by: Prema Jonathan van Win <jonathanvanwin@gmail.com>
1 file changed