include: fix typo

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

diff --git a/src/include/stchrnul.c b/src/include/strchrnul.c
similarity index 100%
rename from src/include/stchrnul.c
rename to src/include/strchrnul.c

diff --git a/src/include/stchrnul.h b/src/include/strchrnul.h
similarity index 100%
rename from src/include/stchrnul.h
rename to src/include/strchrnul.h