clk: meson-g12a: missing break

Add missing break for CLKID_PCIE_PLL in switch statement.

Reported by CppCheck.

Cc: Neil Armstrong <narmstrong@baylibre.com>
Fixes: 08e09c26 ("clk: meson-g12a: Add PCIE PLL support")
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Lukasz Majewski <lukma@denx.de>
Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>