zdb: fix printf format in dump_zap()

When compiling zdb.c on 32-bit platforms, a format conversion error
is reported for a printf() in dump_zap(). Change %l to macro
%" PRIu64 " to match the platform size of a 64-bit unsigned integer.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Martin Matuska <mm@FreeBSD.org>
Closes #16635