ocfs2: llseek requires ocfs2 inode lock for the file in SEEK_END

ocfs2: llseek requires ocfs2 inode lock for the file in SEEK_END

llseek requires ocfs2 inode lock for updating the file size in SEEK_END.
because the file size maybe update on another node.

This bug can be reproduce the following scenario: at first, we dd a test
fileA, the file size is 10k.

on NodeA:
---------
1) open the test fileA, lseek the end of file. and print the position.
2) close the test fileA

on NodeB:
1) open the test fileA, append the 5k data to test FileA.
2) lseek the end of file. and print the position.
3) close file.

At first we run the test program1 on NodeA , the result is 10k.  And then
run the test program2 on NodeB, the result is 15k.  At last, we run the
test program1 on NodeA again, the result is 10k.

After applying this patch the three step result is 15k.

Signed-off-by: Jensen <shencanquan@huawei.com>
Cc: Jie Liu <jeff.liu@oracle.com>
Acked-by: Joel Becker <jlbec@evilplan.org>
Cc: Mark Fasheh <mfasheh@suse.com>
Cc: Sunil Mushran <sunil.mushran@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>