ARM: lpc32xx: stop overwriting TEST_CLK_SEL

While the UDA1380 is described in some lpc3250 device trees, there is
currently no real user of that codec. Anyway, if the codec needs a clock,
it should take it explicitly.

lpc3250_machine_init is called for all the lpc32xx machines and some are
using test1_clk (for example to strobe an HW watchdog). Overwriting
TEST_CLK_SEL prevents booting those platforms.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Tested-by: Gregory CLEMENT <gregory.clement@bootlin.com>
Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>