x86: Optimize loadsegment()

Zero the input register in the exception handler instead of
using an extra register to pass in a zero value.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
LKML-Reference: <1259176706-5908-1-git-send-email-brgerst@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>