i2c/janitoral: drop NO_IRQ from the subsystem

[Wolfram Sang]

Hello,

after having to deal with NO_IRQ confusion more than once, I decided to start a
bit of janitorial work and remove it from the i2c-subsystem. Detail for better
using 0 as "no irq" can be found here: http://lkml.org/lkml/2005/11/21/221

Regards,

   Wolfram