ubifs: Fix some kernel-doc warnings in tnc.c

ubifs: Fix some kernel-doc warnings in tnc.c

Fixes the following W=1 kernel build warning(s):

fs/ubifs/tnc.c:3479: warning: Excess function parameter 'inum' description in 'dbg_check_inode_size'
fs/ubifs/tnc.c:366: warning: Excess function parameter 'node' description in 'lnc_free'

@inum in 'dbg_check_inode_size' should be @inode, fix it.
@node in 'lnc_free' is not in use, Remove it.

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wang Hai <wanghai38@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>