lib/test_printf.c: don't BUG

lib/test_printf.c: don't BUG

BUG is a completely unnecessarily big hammer, and we're more likely to
get the internal bug reported if we just pr_err() and ensure the test
suite fails.

Signed-off-by: Rasmus Villemoes <[email protected]>
Acked-by: Kees Cook <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Andy Shevchenko <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Joe Perches <[email protected]>
Cc: Maurizio Lombardi <[email protected]>
Cc: Tejun Heo <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>