clk: renesas: Fix Realtime Module Stop Control Register offsets

This patch fixes Realtime Module Stop Control Register (RMSTPCR) offsets
based on R-Car Gen3, H2/M2/M2N/E2/E2X hardware user's manual.
The r8a73a4 only has RMSTPCR0 - RMSTPCR5 so this calculation change
doesn't affect it.

Signed-off-by: Hai Pham <hai.pham.ud@renesas.com>
Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>