m32r: Convert print_symbol to %pSR

Use the new vsprintf extension to avoid any possible
message interleaving.

Signed-off-by: Joe Perches <joe@perches.com>
Acked-by: Hirokazu Takata <takata@linux-m32r.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>