blktrace: convert strncpy() to strscpy_pad()

gcc-9 warns about a possibly non-terminated string copy:

kernel/trace/blktrace.c: In function 'do_blk_trace_setup':
kernel/trace/blktrace.c:527:2: error: 'strncpy' specified bound 32 equals destination size [-Werror=stringop-truncation]

Newer versions are fine here because they see the following explicit
nul-termination. Using strscpy_pad() avoids the warning and
simplifies the code a little. The padding helps  give a clean
buffer to userspace.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnd Bergmann <[email protected]>
Acked-by: Justin Stitt <[email protected]>
Cc: Alexey Starikovskiy <[email protected]>
Cc: Bob Moore <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Len Brown <[email protected]>
Cc: Lin Ming <[email protected]>
Cc: Masahiro Yamada <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Nathan Chancellor <[email protected]>
Cc: Nicolas Schier <[email protected]>
Cc: Rafael J. Wysocki <[email protected]>
Cc: "Richard Russon (FlatCap)" <[email protected]>
Cc: Steven Rostedt <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: arndb

kernel/trace/blktrace.c

@@ -524,8 +524,7 @@ static int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
 	if (!buts->buf_size || !buts->buf_nr)
 		return -EINVAL;
 
-	strncpy(buts->name, name, BLKTRACE_BDEV_SIZE);
-	buts->name[BLKTRACE_BDEV_SIZE - 1] = '\0';
+	strscpy_pad(buts->name, name, BLKTRACE_BDEV_SIZE);
 
 	/*
 	 * some device names have larger paths - convert the slashes