tests: drivers: use stm32 dma driver binding macro to configure channel

Use the macro as defined by the
include/zephyr/dt-bindings/dma/stm32_dma.h to configure the
dma channel.
Use the STM32_DMA_PERIPH_TX or STM32_DMA_PERIPH_RX value.

Signed-off-by: Francois Ramu <francois.ramu@st.com>