kprobes: Return error if we fail to reuse kprobe instead of BUG_ON()

kprobes: Return error if we fail to reuse kprobe instead of BUG_ON()

Make reuse_unused_kprobe() to return error code if
it fails to reuse unused kprobe for optprobe instead
of calling BUG_ON().

Signed-off-by: Masami Hiramatsu <[email protected]>
Cc: Anil S Keshavamurthy <[email protected]>
Cc: David S . Miller <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Naveen N . Rao <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: http://lkml.kernel.org/r/153666124040.21306.14150398706331307654.stgit@devbox
Signed-off-by: Ingo Molnar <[email protected]>