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>

drivers/ata/libata-eh.c

@@ -175,8 +175,8 @@ static void ata_eh_handle_port_resume(struct ata_port *ap)
 { }
 #endif /* CONFIG_PM */
 
-static void __ata_ehi_pushv_desc(struct ata_eh_info *ehi, const char *fmt,
-				 va_list args)
+static __printf(2, 0) void __ata_ehi_pushv_desc(struct ata_eh_info *ehi,
+				 const char *fmt, va_list args)
 {
 	ehi->desc_len += vscnprintf(ehi->desc + ehi->desc_len,
 				     ATA_EH_DESC_LEN - ehi->desc_len,