ACPICA: Clarify ACPI_FREE_BUFFER usage.

Add a comment to clarify reason for using ACPI_FREE_BUFFER directly
instead of ACPI_FREE.

In addition to that, change one instance in which ACPI_FREE_BUFFER()
should be used instead of ACPI_FREE().

[rjw: Subject and changelog]
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
diff --git a/drivers/acpi/acpica/nsxfeval.c b/drivers/acpi/acpica/nsxfeval.c
index a6e3bca..ce2a845 100644
--- a/drivers/acpi/acpica/nsxfeval.c
+++ b/drivers/acpi/acpica/nsxfeval.c
@@ -139,7 +139,7 @@
 
 		/* Caller used ACPI_ALLOCATE_BUFFER, free the return buffer */
 
-		ACPI_FREE(return_buffer->pointer);
+		ACPI_FREE_BUFFER(*return_buffer);
 		return_buffer->pointer = NULL;
 	}