Get rid of custom hex_dump_to_buffer().

The output is slightly changed, i.e. each byte followed by white space.

Note, we don't use print_hex_dump() here since the original code uses
nedev_dbg().
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Jie Deng <jiedeng@synopsys.com>
Signed-off-by: David S. Miller <davem@davemloft.net>