bus: arm-ccn: Fix error handling at event allocation
The bitfield allocation function returns error condition
as a negative value, but in two cases its result
was assigned to an unsigned member of the hw_perf_event
structure, thus the error would not be ever detected.
Fixed by using an intermediate, signed variable.
Reported-by: Dan Carpenter <dan.carpenter@oracle.com> Signed-off-by: Pawel Moll <pawel.moll@arm.com> Signed-off-by: Olof Johansson <olof@lixom.net>