ftgmac100: Change interrupt status when a DMA error occurs

ftgmac100: Change interrupt status when a DMA error occurs

The model uses today the "Normal priority transmit buffer unavailable"
interrupt status which it is not appropriate. According to the Aspeed
specs, no interrupts are raised in that case. An "AHB error" status
seems like a better modeling choice for all implementations since it
is covered by the Linux kernel.

Cc: Frederic Konrad <konrad.frederic@yahoo.fr>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Message-Id: <20200819100956.2216690-13-clg@kaod.org>
Signed-off-by: Cédric Le Goater <clg@kaod.org>