It's one character shorter, properly prefixed, and also provides error
detection: %#d triggers a warning.

Done with `sed -i 's/0x%/%#/g' **/*.[ch]` to motivate the use of %#,
existing padding was raised by 2 to account for the counted "0x" (output
should be the same).

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>