cris: kill sys_pipe implementation

The cris implementation of sys_pipe only differs from the generic one
by taking the BKL before calling do_pipe which isn't not nessecary.

Just kill the cris implementation and use the generic one.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>