x86/irq: Get rid of code duplication

commit ab25ac02 upstream.

Reusing an existing vector and assigning a new vector has duplicated
code. Consolidate it.

This is also a preparatory patch for finally plugging the cleanup race.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Borislav Petkov <bp@alien8.de>
Tested-by: Joe Lawrence <joe.lawrence@stratus.com>
Cc: Jiang Liu <jiang.liu@linux.intel.com>
Cc: Jeremiah Mahler <jmmahler@gmail.com>
Cc: andy.shevchenko@gmail.com
Cc: Guenter Roeck <linux@roeck-us.net>
Link: http://lkml.kernel.org/r/20151231160106.721599216@linutronix.de


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>