net: stmmac: dwmac_lib: remove unnecessary checks in dwmac_dma_reset()

it will check the return value of dwmac_dma_reset() in the
stmmac_init_dma_engine() function and report an error if the
return value is not zero. so don't need check here.

Signed-off-by: Dejin Zheng <zhengdejin5@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>