misc: lkdtm: Add volatile to intentional NULL pointer reference
Add a volatile qualifier where a NULL pointer is deliberately
dereferenced to trigger a panic.
Without the volatile qualifier clang will issue the following warning:
"indirection of non-volatile null pointer will be deleted,
not trap [-Wnull-dereference]" and replace the pointer reference
with a __builtin_trap() (which generates a ud2 instruction on x86_64).