ARM: cpuidle: Avoid memleak if init fail

In case there are no DT idle states defined or
cpuidle_register_driver() fails, the copy of the idle driver is leaked:

    unreferenced object 0xede0dc00 (size 1024):
    comm "swapper/0", pid 1, jiffies 4294937431 (age 744.510s)
    hex dump (first 32 bytes):
    94 9e 0b c1 00 00 00 00 00 00 00 00 00 00 00 00 ................
    57 46 49 00 00 00 00 00 00 00 00 00 00 00 00 00 WFI.............
    backtrace:
    [<c1295f04>] arm_idle_init+0x44/0x1ac
    [<c0301e6c>] do_one_initcall+0x3c/0x16c
    [<c1200d70>] kernel_init_freeable+0x110/0x1d0
    [<c0cb3624>] kernel_init+0x8/0x114
    [<c0307a98>] ret_from_fork+0x14/0x3c

So fix this by freeing the unregistered copy in error case.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Fixes: d50a7d8a (ARM: cpuidle: Support asymmetric idle definition)
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>