Add debugging for msr_version.c

The current version of the Makefile had these lines to control debugging.

```
# Uncomment following line(s) to enable debug output from different
# portions of kernel module.
#
#CFLAGS_msr_allowlist.o := -DDEBUG
#CFLAGS_msr_entry.o := -DDEBUG
#CFLAGS_msr_batch.o := -DDEBUG
#CFLAGS_msr-smp.o := -DDEBUG
```

`msr_version.c` never got added.