drivers/virt/fsl_hypervisor: Fix error handling path

First, when memory allocation for sg_list_unaligned failed, there
is a bug of calling put_pages() as we haven't pinned any pages.

Second, if get_user_pages_fast() failed we should unpin num_pinned
pages.

This will address both.

As part of these changes, minor update in documentation.

Fixes: 6db71994 ("drivers/virt: introduce Freescale hypervisor management driver")
Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Link: https://lore.kernel.org/r/1598995271-6755-1-git-send-email-jrdr.linux@gmail.com


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