device-tree: fix infinite loop issue in 'assign_shared_memory()'

Fix an issue in the 'fail:' cleanup path of the 'assign_shared_memory()'
function where the use of an unsigned long 'i' with the condition
'--i >= 0' caused an infinite loop. Update the loop to use 'i--',
ensuring correct loop termination.

This change adheres to MISRA C Rule 14.3: "Controlling expressions shall
not be invariant."

Fixes: 041957bad3 ("xen/arm: Add additional reference to owner domain when the owner is allocated")
Signed-off-by: Dmytro Prokopchuk <dmytro_prokopchuk1@epam.com>
Acked-by: Michal Orzel <michal.orzel@amd.com>

xen/common/device-tree/static-shmem.c

@@ -185,7 +185,7 @@ static int __init assign_shared_memory(struct domain *d, paddr_t gbase,
     return 0;
 
  fail:
-    while ( --i >= 0 )
+    while ( i-- )
         put_page_nr(page + i, nr_borrowers);
     return ret;
 }