ext4: use BIT() macro for BH_** state bits

Simply use BIT() macro for all BH_** state bits instead of open
coding it.

There should be no functionality change in this patch.

Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
Link: https://lore.kernel.org/r/57667689f51a3f9dba2fcef7d3425187fa3ba69f.1589086800.git.riteshh@linux.ibm.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>