xen: fail gnttab_grow_table() in case of missing allocations

xen: fail gnttab_grow_table() in case of missing allocations

In case gnttab_grow_table() is being called without
grant_table_set_limits() having been called for the domain, e.g. in
case of a toolstack error, fail the function instead of crashing the
system.

While at it let gnttab_grow_table() return a proper error code instead
of 1 for success.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>