prlimit.c: Fix careless use of `lt' variable.

prlimit.c: Fix careless use of `lt' variable.

The `lt' variable is used in the second pass for actually printing
limits, but its value is simply debris from the first command-line
parsing pass and has no useful meaning.

Since it's a convenient abbreviation, initialize it properly in the
second-pass loop and use it consistently.

Spotted by GCC.