mesa: Don't compare unsigned for < 0

mesa: Don't compare unsigned for < 0

The INTEL_performance_query spec says

   "Performance counter id 0 is reserved as an invalid counter."

GLuint counterid_to_index(GLuint counterid) just returns counterid - 1,
so with unsigned overflow rules, it will generate 0xFFFFFFFF given an
input of 0. 0xFFFFFFFF will trigger the counterIndex >= queryNumCounters
check, so the code worked as is. It just contained a useless comparison.

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>