ARM: 9229/1: amba: Fix use-after-free in amba_read_periphid()

After commit f2d3b9a4 ("ARM: 9220/1: amba: Remove deferred device
addition"), it became possible for amba_read_periphid() to be invoked
concurrently from two threads for a particular AMBA device.

Consider the case where a thread (T0) is registering an AMBA driver, and
searching for all of the devices it can match with on the AMBA bus.
Suppose that another thread (T1) is executing the deferred probe work,
and is searching through all of the AMBA drivers on the bus for a driver
that matches a particular AMBA device. Assume that both threads begin
operating on the same AMBA device and the device's peripheral ID is
still unknown.

In this scenario, the amba_match() function will be invoked for the
same AMBA device by both threads, which means amba_read_periphid()
can also be invoked by both threads, and both threads will be able
to manipulate the AMBA device's pclk pointer without any synchronization.
It's possible that one thread will initial...