MAINTAINERS: add Nick as Reviewer for compiler_attributes.h

$ ./scripts/get_maintainer.pl --rolestats --git-blame -f \
  include/linux/compiler_attributes.h
...
Nick Desaulniers <ndesaulniers@google.com> (supporter:CLANG/LLVM BUILD
SUPPORT,authored lines:43/331=13%,commits:8/15=53%)

It's also important for me to stay up on which compiler attributes clang
is missing.

Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>