mfd: stpmic1: Fixup main control register and bits naming

Fixup main control register and bits naming so the match the naming from
the datasheet.

https://www.st.com/resource/en/datasheet/stpmic1.pdf



Signed-off-by: Sean Nyekjaer <sean@geanix.com>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230602062426.3947116-1-sean@geanix.com