clk: lpc32xx: do not register clock "0"

The following errors are display in the console during the power-on:
[    0.000000] lpc32xx_usb_clk_init: failed to register (null) clock: -12
[    0.000000] lpc32xx_clk_init: failed to register (null) clock: -12

There is no need to register clock "0"; the first clock used is 1;

Signed-off-by: Sylvain Lemieux <slemieux@tycoint.com>
Acked-by: Vladimir Zapolskiy <vz@mleia.com>
[sboyd@codeaurora.org: s/prepare/register/]
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>