scsi: print single-character strings with seq_putc

Using seq_putc to print a single character saves at least a strlen()
call and a memory access, and may also give a small .text reduction.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: Finn Thain <fthain@telegraphics.com.au>
Signed-off-by: Christoph Hellwig <hch@lst.de>