regulator: da9210: Mask all interrupt sources to deassert interrupt line

After boot-up, some events may be set, and cause the da9210 interrupt
line to be asserted. As the da9210 driver doesn't have interrupt support
yet, this causes havoc on systems where the interrupt line is shared
among multiple devices.

This is the case on e.g. r8a7791/koelsch, where the interrupt line is
shared with a da9063 regulator, and the following events are set:

    EVENT_A = 0x00000011 (GPI0 | GPI4)
    EVENT_B = 0x00000002 (NPWRGOOD)

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Mark Brown <broonie@kernel.org>