dmaengine: ti: k3-udma: Do not use ring_get_occ in udma_pop_from_ring

The ring_get_occ is redundant as the k3_ringacc_ring_pop() is also
checking the occ of the ring.

With removing the ring_get_occ, the function can be simplified as well.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>