dio: return -ENOMEM when kzalloc() fails

Return -ENOMEM when kzalloc() fails in order to inform the caller of the
failure.

Signed-off-by: Salah Triki <salah.triki@gmail.com>
Link: https://lore.kernel.org/r/20210702133114.GA314157@pc


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>