rsi: Add pr_fmt,__printf, fix format & arg mismatch

Emit a prefix for the rsi_dbg messages.

Fix the format and argument mismatch and add
__printf(2, 3) to try to avoid more.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>