clk: remove duplicated COMMON_CLK_NXP record from clk/Kconfig

Presumably the second COMMON_CLK_NXP config option in
drivers/clk/Kconfig appeared after a merge conflict resolution, remove
the wrong record of two.

Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>