sparc: fix format string argument for prom_printf()

prom_printf() takes printf style arguments.  Specifing GCC's format
attribute reveals that there are several wrong usages of prom_printf().

This fixes those wrong format strings and arguments, and also leaves
format attributes in order to detect similar mistakes at compile time.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: sparclinux@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>