VFS/fsstack: handle 32-bit smp + preempt + large files in fsstack_copy_inode_size

Copy the inode size and blocks from one inode to another correctly on 32-bit
systems with CONFIG_SMP, CONFIG_PREEMPT, or CONFIG_LBDAF.  Use proper inode
spinlocks only when i_size/i_blocks cannot fit in one 32-bit word.

Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Erez Zadok <ezk@cs.sunysb.edu>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>