x86, trivial: Fix grammo in tsc comment about Geode TSC reliability

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
Cc: marcelo@kvack.org
Cc: dilinger@collabora.co.uk
Cc: trivial@kernel.org
LKML-Reference: <1263764685-9871-1-git-send-email-cascardo@holoscopio.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>