There is no need to have a duplication of the generic library, i.e.
hex2bin().

Replace the open coded variant.
Signed-off-by: NAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: NBart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: NJason Gunthorpe <jgg@mellanox.com>