[S390] qdio: prevent handling of buffers if count is zero
[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 <91a6ce52bf23f30aed3c81da3c0c6b8e332ad699@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <52616596d8f5df0d597e85ab515377f92f939c68@de.ibm.com>

TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas