binfmt_flat: Use %u to format u32

Several variables had their types changed from unsigned long to u32, but
the printk()-style format to print them wasn't updated, leading to:

    fs/binfmt_flat.c: In function ‘load_flat_file’:
    fs/binfmt_flat.c:577: warning: format ‘%ld’ expects type ‘long int’, but argument 3 has type ‘u32’

Fixes: 468138d7 ("binfmt_flat: flat_{get,put}_addr_from_rp() should be able to fail")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>