Instead of printing bytes one by one, let's use %phN to print the buffer in
one go.

Also use hweight8 to count number of partitions instead of inspecting it
bit by bit.
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Tested-by: Nick Dyer <nick@shmanahar.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>