staging/lustre/llite: Adjust NULL comparison codestyle

staging/lustre/llite: Adjust NULL comparison codestyle

All instances of "x == NULL" are changed to "!x" and
"x != NULL" to "x"

The only exception is ll_update_inode where dropping != NULL
in the construction below would break the logic.
I guess we could change lsm != NULL to !!lsm, but that's uglier.
(lsm != NULL) == ((body->valid & OBD_MD_FLEASIZE) != 0)

Also removed some redundant assertions.

Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>