ata: libata-core: fix parameter type in ata_xfer_mode2shift()

The data transfer mode that corresponds to the 'xfer_mode' parameter for
ata_xfer_mode2shift() is a 8-bit *unsigned* value.  Using *unsigned long*
to declare the parameter leads to a problematic implicit *int* to *unsigned
long* cast and was most probably a result of a copy/paste mistake -- use
the 'u8' type instead, as in ata_xfer_mode2mask()...

Found by Linux Verification Center (linuxtesting.org) with the SVACE static
analysis tool.
Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>

drivers/ata/libata-core.c

@@ -898,7 +898,7 @@ EXPORT_SYMBOL_GPL(ata_xfer_mode2mask);
  *	RETURNS:
  *	Matching xfer_shift, -1 if no match found.
  */
-int ata_xfer_mode2shift(unsigned long xfer_mode)
+int ata_xfer_mode2shift(u8 xfer_mode)
 {
 	const struct ata_xfer_ent *ent;
 

include/linux/libata.h

@@ -1110,7 +1110,7 @@ extern void ata_unpack_xfermask(unsigned long xfer_mask,
 			unsigned long *udma_mask);
 extern u8 ata_xfer_mask2mode(unsigned long xfer_mask);
 extern unsigned long ata_xfer_mode2mask(u8 xfer_mode);
-extern int ata_xfer_mode2shift(unsigned long xfer_mode);
+extern int ata_xfer_mode2shift(u8 xfer_mode);
 extern const char *ata_mode_string(unsigned long xfer_mask);
 extern unsigned long ata_id_xfermask(const u16 *id);
 extern int ata_std_qc_defer(struct ata_queued_cmd *qc);