__printf is useful to verify format and arguments. Remove the following
warning (with W=1):

  drivers/ata/libata-eh.c:183:10: warning: function might be possible candidate for ‘gnu_printf’ format attribute [-Wsuggest-attribute=format]
Signed-off-by: NMathieu Malaterre <malat@debian.org>
Signed-off-by: NTejun Heo <tj@kernel.org>