genirq: Fix spurious irq seqfile conversion

single_open data argument must be PDE(inode)->data instead of NULL
otherwise seq_file->private is always NULL and we always read the
spurious data of irq 0.

Reported-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>