xfs/122: escape %zu in printf with %% not \\%

xfs/122: escape %zu in printf with %% not \\%

The standard way to escape % in a printf is with %%; although \\%zu
seems to have worked in awk until recently, an upgrade on Fedora 36
has started failing:

awk: cmd. line:1: (FILENAME=- FNR=1) fatal: not enough arguments to satisfy format string
        'printf("sizeof(%s) = \%zu\n", sizeof(%s));
    '
                                              ^ ran out for this one
Switching the escape to "%%" fixes this for me, and also works
on my very old RHEL7 mcahine.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>