esp: allow non-DMA callback in esp_transfer_data() initial transfer

esp: allow non-DMA callback in esp_transfer_data() initial transfer

The current implementation only resumes DMA transfers when incoming data is
received from the target device, but this is also required for non-DMA transfers
with the next set of non-DMA changes.

Rather than duplicate the DMA/non-DMA dispatch logic in the initial transfer
section, update the code so that the initial transfer section can just
fallthrough to the main DMA/non-DMA dispatch logic.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Message-Id: <20210519100803.10293-2-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>