pinctrl: renesas: rcar: Avoid changing PUDn when disabling bias

When disabling pin bias, there is no need to touch the LSI pin
pull-up/down control register (PUDn), which selects between pull-up and
pull-down.  Just disabling the pull-up/down function through the LSI pin
pull-enable register (PUENn) is sufficient.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Link: https://lore.kernel.org/r/071ec644de2555da593a4531ef5d3e4d79cf997d.1625064076.git.geert+renesas@glider.be