mfd: tps65217: Update register interrupt mask bits instead of writing operation

TPS65217 interrupt register includes read/writeable mask bits with
read-only status bits. (bit 4, 5, 6 are R/W, bit 0, 1, 2 are RO)
And reserved bit is not required.

Register update operation is preferred for disabling all interrupts during
the device initialisation.

Signed-off-by: Milo Kim <woogyom.kim@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>