findmnt: revise the code for -I and -D option

findmnt: revise the code for -I and -D option

Fixes #2913.

3dd79293b5b655da9d913dedd8facb08959a7826 added -I option.
However, the code used bit flags (FL_DF and FL_DF_INODES) wrongly;
the code broke the output of -D option.

Signed-off-by: Masatake YAMATO <yamato@redhat.com>
(cherry picked from commit aa0c45e8686df509c169121473d2cfb4fe18c3ea)

Gbp-Pq: Topic upstream
Gbp-Pq: Name findmnt-revise-the-code-for-I-and-D-option.patch