gnttab: don't cast away constness

While _set_status_v2() indeed doesn't alter the grant_entry_header_t it
is handed a pointer to, _set_status_v1() does. Drop the const from the
parameter of the latter (and then necessarily also from _set_status()'s),
while adding const to the local variable of the former.

No functional change.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Roger Pau Monné <roger@xenproject.org>

xen/common/grant_table.c

@@ -740,7 +740,7 @@ static unsigned int nr_grant_entries(struct grant_table *gt)
     return 0;
 }
 
-static int _set_status_v1(const grant_entry_header_t *shah,
+static int _set_status_v1(grant_entry_header_t *shah,
                           struct domain *rd,
                           struct active_grant_entry *act,
                           int readonly,
@@ -832,7 +832,7 @@ static int _set_status_v2(const grant_entry_header_t *shah,
                           domid_t  ldomid)
 {
     int      rc    = GNTST_okay;
-    uint32_t *raw_shah = (uint32_t *)shah;
+    const uint32_t *raw_shah = (const uint32_t *)shah;
     union grant_combo scombo;
     uint16_t mask  = GTF_type_mask;
 
@@ -909,7 +909,7 @@ done:
 }
 
 
-static int _set_status(const grant_entry_header_t *shah,
+static int _set_status(grant_entry_header_t *shah,
                        grant_status_t *status,
                        struct domain *rd,
                        unsigned int rgt_version,