compiler: Fix up oversight with transfer size calculation

Author: EdCaunt

devito/passes/iet/langbase.py

@@ -12,7 +12,7 @@
 from devito.mpi.distributed import MPICommObject
 from devito.passes import is_on_device
 from devito.passes.iet.engine import iet_pass
-from devito.symbolics import Byref, CondNe, SizeOf
+from devito.symbolics import Byref, CondNe, SizeOf, as_long
 from devito.tools import as_list, is_integer, prod
 from devito.types import QueueID, Symbol, Wildcard
 
@@ -538,7 +538,7 @@ def __new__(cls, function, *args):
 
     @property
     def size(self):
-        return prod(s for _, s in self)
+        return as_long(prod(s for _, s in self))
 
     @property
     def nbytes(self):