linux-wandboard

[S390] qdio: prevent handling of buffers if count is zero

Exit do_QDIO early if the buffer count is zero to prevent side effects
in the following functions.

Signed-off-by: Jan Glauber <jang@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>