dma: ti: k3-udma: add missing <net.h> include

net.h is needed for PKTBUFSRX. Without this definition, the driver will
always use 4 RX buffers, causing am65-cpsw-nuss initialization to fail
when a higher number of buffers is requested.

Signed-off-by: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>