target-i386: Allow tsc-frequency to be larger then 2.147G

The check using INT_MAX (2147483647) is wrong in this case.

Signed-off-by: Fred Oliveira <foliveira@cloudswitch.com>
Signed-off-by: Don Slutz <Don@CloudSwitch.com>
Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
