pvgrub: initialise p2m_size

In 84083790 ("libxc: add p2m_size to xc_dom_image") a new field is
added. We should initialised this field in pvgrub as well, otherwise
xc_dom_build_image won't work properly.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

stubdom/grub/kexec.c

@@ -276,12 +276,13 @@ void kexec(void *kernel, long kernel_size, void *module, long module_size, char
     dom->total_pages = start_info.nr_pages;
 
     /* equivalent of arch_setup_meminit */
+    dom->p2m_size = dom->total_pages;
 
     /* setup initial p2m */
-    dom->p2m_host = malloc(sizeof(*dom->p2m_host) * dom->total_pages);
+    dom->p2m_host = malloc(sizeof(*dom->p2m_host) * dom->p2m_size);
 
     /* Start with our current P2M */
-    for (i = 0; i < dom->total_pages; i++)
+    for (i = 0; i < dom->p2m_size; i++)
         dom->p2m_host[i] = pfn_to_mfn(i);
 
     if ( (rc = xc_dom_build_image(dom)) != 0 ) {