rtl8xxxu: tuse %*ph to dump buffers

Use %*ph specifier to dump small buffers in hex format instead of doing this
byte-by-byte.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>