vfs: delete surplus inode NULL check

Each iteration of d_delete we reload inode from dentry->d_inode and
then call S_ISDIR(inode-i_mode), so inode cannot possibly be NULL
shortly afterwards unless something went horribly wrong.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>