ide-cd: Do not access completed requests in the irq handler

ide_cd_error_cmd() can complete an erroneous request with leftover
buffers. Signal this with its return value so that the request is not
accessed after its completion in the irq handler and we oops.

Cc: <stable@kernel.org> # 32.x 33.x 34.x
Signed-off-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: David S. Miller <davem@davemloft.net>