xen/grant-table: add error-handling code on failure of gnttab_resume

Jump to the label ini_nomem as done on the failure of the page allocations
above.

The code at ini_nomem is modified to accommodate different return values.

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>