Optimize the code that copies strings

Optimize the code that copies strings

Using strncpy() to copy strings is suboptimal because strncpy writes a
bunch of additional unnecessary null bytes. Use snprintf() instead of
strncpy(). An additional advantage of snprintf() is that it guarantees
that the output string is '\0'-terminated.

This patch is an improvement for commit 32e31c8c5f7b ("Fix string copy
compilation warnings").

Cc: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>