hw/net/dp8393x: Avoid unintentional sign extensions on addresses

hw/net/dp8393x: Avoid unintentional sign extensions on addresses

The dp8393x has several 32-bit values which are formed by concatenating
two 16 bit device register values. Attempting to do these inline
with ((s->reg[HI] << 16) | s->reg[LO]) can result in an unintended
sign extension because "x << 16" is of type 'int' even though s->reg
is unsigned, and so if the expression is used in a context where
it is cast to uint64_t the value is incorrectly sign-extended.
Fix this by using accessor functions with a uint32_t return type;
this also makes the code a bit easier to read.

This should fix Coverity issues 1307765, 1307766, 1307767, 1307768.

(To avoid having a ctda read function only used in a DPRINTF,
we move the DPRINTF down slightly so it can use the ttda function.)

Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Tested-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Hervé Poussineau <hpoussin@reactos.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Jason Wang <jasowang@redhat.com>