nfs: Don't busy-wait on SIGKILL in __nfs_iocounter_wait

nfs: Don't busy-wait on SIGKILL in __nfs_iocounter_wait

commit 92a56555bd576c61b27a5cab9f38a33a1e9a1df5 upstream.

If a SIGKILL is sent to a task waiting in __nfs_iocounter_wait,
it will busy-wait or soft lockup in its while loop.
nfs_wait_bit_killable won't sleep, and the loop won't exit on
the error return.

Stop the busy-wait by breaking out of the loop when
nfs_wait_bit_killable returns an error.

Signed-off-by: David Jeffery <djeffery@redhat.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Cc: Neil Brown <nfbrown@suse.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>