driver core: add __printf verification to __ata_ehi_pushv_desc

__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: Mathieu Malaterre <malat@debian.org>
Signed-off-by: Tejun Heo <tj@kernel.org>