block/partitions/ldm: convert strncpy() to strscpy()

The strncpy() here can cause a non-terminated string, which older gcc
versions such as gcc-9 warn about:

In function 'ldm_parse_tocblock',
inlined from 'ldm_validate_tocblocks' at block/partitions/ldm.c:386:7,
inlined from 'ldm_partition' at block/partitions/ldm.c:1457:7:
block/partitions/ldm.c:134:2: error: 'strncpy' specified bound 16 equals destination size [-Werror=stringop-truncation]
134 | strncpy (toc->bitmap1_name, data + 0x24, sizeof (toc->bitmap1_name));
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
block/partitions/ldm.c:145:2: error: 'strncpy' specified bound 16 equals destination size [-Werror=stringop-truncation]
145 | strncpy (toc->bitmap2_name, data + 0x46, sizeof (toc->bitmap2_name));
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

New versions notice that the code is correct after all because of the
following termination, but replacing the strncpy() with strscpy_pad()
or strcpy() avoids the warning and simplifies the code at the same time.

Use the padding version here to keep the existing behavior, in case
the code relies on not including uninitialized data.

Link: https://lkml.kernel.org/r/20240409140059.3806717-4-arnd@kernel.org
Reviewed-by: Justin Stitt <justinstitt@google.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Alexey Starikovskiy <astarikovskiy@suse.de>
Cc: Bob Moore <robert.moore@intel.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Len Brown <lenb@kernel.org>
Cc: Lin Ming <ming.m.lin@intel.com>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nicolas Schier <nicolas@fjasle.eu>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: "Richard Russon (FlatCap)" <ldm@flatcap.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>