The result of xchg() is not used, and in addition it is used on a one byte
memory area which leads to inefficient code.
Use WRITE_ONCE() instead to achieve the same result with much less
generated code.
Acked-by: Harald Freudenberger <freude@linux.ibm.com>
Acked-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>