dcache.c: get rid of pointless macros

D_HASH{MASK,BITS} are used once each, both in the same function (d_hash()).
At this point they are actively misguiding - they imply that values are
compiler constants, which is no longer true.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --cc fs/dcache.c
Simple merge