x86: Replace the EVT_TO_HPET_DEV() macro with an inline function

The original macro worked only when applied to variables named
'evt'. While this could have been fixed by simply renaming the
macro argument, a more type-safe replacement is preferred.

Signed-off-by: Ferenc Wagner <wferi@niif.hu>
Cc: Venkatesh Pallipadi \(Venki\) <venki@google.com>
Link: http://lkml.kernel.org/r/8ed5c66c02041226e8cf8b4d5d6b41e543d90bd6.1321626272.git.wferi@niif.hu
Signed-off-by: Ingo Molnar <mingo@elte.hu>