lib: fix implicit users of kernel.h for TAINT_WARN

A pending header cleanup will cause this to show up as:

lib/average.c:38: error: 'TAINT_WARN' undeclared (first use in this function)
lib/list_debug.c:24: error: 'TAINT_WARN' undeclared (first use in this function)

and TAINT_WARN comes from include/linux/kernel.h file.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>