drm/radeon: use raw buffer printk specifier

printk format strings accepting a single subsequent argument
are shorter thus easier to read.

Instead of having format strings accepting 3 different arguments
pointing to first 3 bytes of the same buffer rewrite the format
string to accept only one argument - the buffer - with "%3ph"
specifier.

Signed-off-by: Dmitry Rozhkov <dmitry.rozhkov@linux.intel.com>
Suggested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>