tpm: simplify code by using %*phN specifier

Instead of looping by ourselves we may use %*phN specifier to dump a small
buffer.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
[ PHuewe: removed now unused variable i ]
Signed-off-by: Peter Huewe <peterhuewe@gmx.de>