mfd: Fix tps65910 section annotations

A warning was being generated by the reference from tps65910_i2c_probe()
to tps65910_sleepinit() since the latter was annotated as __init but the
former was unannotated. Since these functions can only be called during
device init make them both __devinit, and while we're at it also annotate
tps65910_i2c_remove() __devexit for symmetry.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>