memory: renesas-rpc-if: simplify register update

No need to open code regmap_update_bits().

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Tested-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Link: https://lore.kernel.org/r/20211117102902.20062-1-wsa+renesas@sang-engineering.com


Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>