esp.c: replace get_cmd() with esp_do_nodma()

esp.c: replace get_cmd() with esp_do_nodma()

Now that the esp_do_nodma() state machine correctly handles incoming FIFO
data, all remaining users of get_cmd() can be replaced with esp_do_nodma()
and the get_cmd() function removed completely.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Tested-by: Helge Deller <deller@gmx.de>
Tested-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20240112125420.514425-68-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>