ocfs2: char is not always signed

Commit 1c66b360 (Change some lock status member in ocfs2_lock_res
to char.)  states that these fields need to be signed due to comparision
to -1, but only changed the type from unsigned char to char.   However, it
is a compiler option if char is a signed or unsigned type.  Change these
fields to signed char so the code will work with all compilers.

Signed-off-by: Milton Miller <miltonm@bga.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>