Get rid of the own atomic_sub_return() implementation. Otherwise we can't
make use of the interlocked-access facility 1 instructions for
atomic_sub_return(), since there is no "load and subtract" instruction
available.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>