clk: nxp: Select MFD_SYSCON for creg driver

Commit 378523d1 ("clk: add lpc18xx creg clk driver")
added a new clock driver but missed the proper MFD_SYSCON select.
Fix it.

Fixes: 378523d1 ("clk: add lpc18xx creg clk driver")
Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Acked-by: Joachim Eastwood <manabian@gmail.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>