journal/journald-console: fix format-specifier issue

journal/journald-console: fix format-specifier issue

timespec::tv_nsec can have different sizes depending on the
host architecture. On x32 in particular, it is 8 bytes long
while the long int type is only 4 bytes long. Hence, using
ld as a format specifier will trigger a format error. Thus,
explicitly cast timespec::tv_nsec to nsec_t and use PRI_NSEC
as the format specifier to make sure the sizes for both match.