mfd: tps65090: Fix enum in header file

The enum is missing the definition for the first bit, which makes all
the rest off by one. Add definition for the TPS65090_IRQ_INTERRUPT bit
which at 0.

Signed-off-by: Rhyland Klein <rklein@nvidia.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>