scsi: libsas: remove private hex2bin() implementation

The function sas_parse_addr() could be easily substituted by hex2bin()
which is in kernel library code.

Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Tested-by: Xiang Chen <chenxiang66@hisilicon.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>