clk: nxp: lpc18xx: Initialize clk_init_data::flags to 0

Failure to initialize this flag to 0 by default can result in
stack junk filling the clk_init_data structure and weird things
happen. Joachim noticed that the critical clk feature started
triggering for these clks causing boot failures, when it really
shouldn't have happened:

BUG: scheduling while atomic: swapper/0/0x00000002
CPU: 0 PID: 0 Comm: swapper Not tainted
4.6.0-rc6-next-20160505-00001-g5c8320450d1c #826
Hardware name: NXP LPC18xx/43xx (Device Tree)
[<2800be81>] (unwind_backtrace) from [<2800b22f>] (show_stack+0xb/0xc)
[<2800b22f>] (show_stack) from [<2801ea21>] (__schedule_bug+0x2d/0x44)
[<2801ea21>] (__schedule_bug) from [<281dc937>] (__schedule+0x3b/0x268)
[<281dc937>] (__schedule) from [<281dcbbb>] (schedule+0x57/0x64)
[<281dcbbb>] (schedule) from [<281de8ef>] (schedule_timeout+0xfb/0x120)
[<281de8ef>] (schedule_timeout) from [<28030fcd>] (msleep+0xf/0x12)
[<28030fcd>] (msleep) from [<28165a6d>] (clk_creg_32k_prepare+0x1f/0x24)
[<28165a...