i2c-mpc: Compare to NO_IRQ instead of zero

Alter the mpc i2c driver to use the NO_IRQ symbol instead of the constant
zero when checking for valid interrupts. NO_IRQ=-1 on ppc and NO_IRQ=0 on
powerpc so the checks against zero are not correct.

Signed-off-by: Jon Smirl <jonsmirl@gmail.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>