fs/xfs: replace strncpy with memtostr_pad()

fs/xfs: replace strncpy with memtostr_pad()

Replace the deprecated strncpy() with memtostr_pad(). This also avoids
the need for separate zeroing using memset(). Mark sb_fname buffer with
__nonstring as its size is XFSLABEL_MAX and so no terminating NULL for
sb_fname.

Signed-off-by: Pranav Tyagi <pranav.tyagi03@gmail.com>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>