clang-tidy: replace NULL/0 with nullptr

Adopt C++11 nullptr for pointer initialization and null checks,
replacing 0/NULL. Improves readability, avoids implicit integer
conversions, and aligns with clang-tidy modernize-use-nullptr.
No functional behavior changes.

Change-Id: I12c451c6c96a788f182982c6a90a377f4ed2b568
Signed-off-by: Jayanth Othayoth <ojayanth@gmail.com>
3 files changed