afs: Return -EAGAIN, not -EREMOTEIO, when a file already locked

afs: Return -EAGAIN, not -EREMOTEIO, when a file already locked

When trying to get a file lock on an AFS file, the server may return
UAEAGAIN to indicate that the lock is already held.  This is currently
translated by the default path to -EREMOTEIO.

Translate it instead to -EAGAIN so that we know we can retry it.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeffrey E Altman <jaltman@auristor.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
Link: https://lore.kernel.org/r/166075761334.3533338.2591992675160918098.stgit@warthog.procyon.org.uk/
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>