kprobes: Remove pointless BUG_ON() from reuse_unused_kprobe()

Since reuse_unused_kprobe() is called when the given kprobe
is unused, checking it inside again with BUG_ON() is
pointless. Remove it.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Cc: David S . Miller <davem@davemloft.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Naveen N . Rao <naveen.n.rao@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/153666121154.21306.17540752948574483565.stgit@devbox


Signed-off-by: Ingo Molnar <mingo@kernel.org>