gpumon.ml: fix incorrect word in error message
gpumon.ml: fix incorrect word in error message

I accidentally renamed the "Config" word in that error message when
using sed to rename the Config module to Gpumon_config.

Signed-off-by: Gabor Igloi <7535f5501fd71876c93d896691e178fd3a11cfbb@citrix.com>

xenserver/gpumon