x86: Fix 32-bit MSI-X allocation leakage

This bug was introduced in the 2.6.24 i386/x86_64 tree merge, where
MSI-X vector allocation will eventually fail.  The cause is the new
bit array tracking used vectors is not getting cleared properly on
IRQ destruction on the 32-bit APIC code.

This can be seen easily using the ixgbe 10 GbE driver on multi-core
systems by simply loading and unloading the driver a few times.
Depending on the number of available vectors on the host system, the
MSI-X allocation will eventually fail, and the driver will only be
able to use legacy interrupts.

I am generating the same patch for both stable trees for 2.6.24 and
2.6.25.

Signed-off-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>