CLEANUP: debug: mark the RNG's seed as unsigned

Since commit 8a069eb9a ("MINOR: debug: add a trivial PRNG for scheduler
stress-tests"), 32-bit gcc 4.7 emits this warning when parsing the
initial seed for the debugger's RNG (2463534242):

  src/debug.c:46:1: warning: this decimal constant is unsigned only in ISO C90 [enabled by default]

Let's mark it explicitly unsigned.
1 file changed