lib/ext2fs: consistently use #ifdefs in ext2fs_print_bmap_statistics()

lib/ext2fs: consistently use #ifdefs in ext2fs_print_bmap_statistics()

Since the 'now' variable is only used to calculate 'inuse', and 'inuse'
is only used when defined(ENABLE_BMAP_STATS_OPS), it makes sense to
guard the declaration and initialization of 'now' and 'inuse' by the
same condition, just like the '*_perc' variables in the same function.

This addresses the following compiler warning with clang -Wall:

        double inuse;
               ^

gen_bitmap64.c:187:9: warning: variable 'inuse' set but not used [-Wunused-but-set-variable]
Reviewed-by: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>