x86, hpet: Fix bogus error check in hpet_assign_irq()

create_irq() returns -1 if the interrupt allocation failed, but the
code checks for irq == 0.

Use create_irq_nr() instead.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Venkatesh Pallipadi <venki@google.com>
LKML-Reference: <alpine.LFD.2.00.1009282310360.2416@localhost6.localdomain6>
Cc: stable@kernel.org
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>