fs/hfsplus/xattr.c: replace strncpy with memcpy

fs/hfsplus/xattr.c: replace strncpy with memcpy

strncpy() was used to copy a fixed size buffer.  Since NUL-terminating
string is not required here, prefer a memcpy function.  The generated
code (ppc32) remains the same.

Silence the following warning triggered using W=1:

  fs/hfsplus/xattr.c:410:3: warning: 'strncpy' output truncated before terminating nul copying 4 bytes from a string of the same length [-Wstringop-truncation]

Link: http://lkml.kernel.org/r/20190529113341.11972-1-malat@debian.org
Signed-off-by: Mathieu Malaterre <malat@debian.org>
Reviewed-by: Vyacheslav Dubeyko <slava@dubeyko.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>