Impact: fix bootup crash

Even though it tested fine for me, there was still a bug in the
first patch: I have overlooked a call to ptregscall_common. This
patch fixes that, I think, but the code is never executed for
me while running a debian install... (I tested this by putting
an "1:jmp 1b" in there.)
Signed-off-by: Ingo Molnar <mingo@elte.hu>