hfsplus: fix out-of-bounds warnings in __hfsplus_setxattr

hfsplus: fix out-of-bounds warnings in __hfsplus_setxattr

Fix the following out-of-bounds warnings by enclosing structure members
file and finder into new struct info:

fs/hfsplus/xattr.c:300:5: warning: 'memcpy' offset [65, 80] from the object at 'entry' is out of the bounds of referenced subobject 'user_info' with type 'struct DInfo' at offset 48 [-Warray-bounds]
fs/hfsplus/xattr.c:313:5: warning: 'memcpy' offset [65, 80] from the object at 'entry' is out of the bounds of referenced subobject 'user_info' with type 'struct FInfo' at offset 48 [-Warray-bounds]

Refactor the code by making it more "structured."

Also, this helps with the ongoing efforts to enable -Warray-bounds and
makes the code clearer and avoid confusing the compiler.

Matthew said:

: The offending line is this:
:
: -                               memcpy(&entry.file.user_info, value,
: +                               memcpy(&entry.file.info, value,
:                                                 file_finderinfo_len);
:
: what it's trying to do is copy two structs which are adjacent to each
: other in a single call to memcpy().  gcc legitimately complains that
: the memcpy to this struct overruns the bounds of the struct.  What
: Gustavo has done here is introduce a new struct that contains the two
: structs, and now gcc is happy that the memcpy doesn't overrun the
: length of this containing struct.

Link: https://github.com/KSPP/linux/issues/109
Link: https://lkml.kernel.org/r/20210330145226.GA207011@embeddedor
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reported-by: kernel test robot <lkp@intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>