ACPICA: Fix miscellaneous warnings under gcc 4+

Some possible warnings with gcc 4+, especially with extended warnings
enabled

Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lin Ming <ming.m.lin@intel.com
Signed-off-by: Len Brown <len.brown@intel.com>
diff --git a/drivers/acpi/acpica/dsobject.c b/drivers/acpi/acpica/dsobject.c
index dab3f48..02e6caa 100644
--- a/drivers/acpi/acpica/dsobject.c
+++ b/drivers/acpi/acpica/dsobject.c
@@ -734,7 +734,8 @@
 
 			/* Local ID (0-7) is (AML opcode - base AML_LOCAL_OP) */
 
-			obj_desc->reference.value = opcode - AML_LOCAL_OP;
+			obj_desc->reference.value =
+			    ((u32)opcode) - AML_LOCAL_OP;
 			obj_desc->reference.class = ACPI_REFCLASS_LOCAL;
 
 #ifndef ACPI_NO_METHOD_EXECUTION
@@ -754,7 +755,7 @@
 
 			/* Arg ID (0-6) is (AML opcode - base AML_ARG_OP) */
 
-			obj_desc->reference.value = opcode - AML_ARG_OP;
+			obj_desc->reference.value = ((u32)opcode) - AML_ARG_OP;
 			obj_desc->reference.class = ACPI_REFCLASS_ARG;
 
 #ifndef ACPI_NO_METHOD_EXECUTION