imx/gpt.c allocate_register_callback asserts instead of returning an error

[bennoleslie]

In the allocate_register_callback function there is an assert:

    assert(curr_num == 0);

This does not seem appropriate. I'd suggest that this should return an error (in the same way that if ps_pmem_map fails an error is returned). The function has no reasonable basis on which to assert curr_num as the FDT contents are well outside the control. (By contrast the assertion assert(token != NULL) seems reasonable as this is controlled by the call to ps_fdt_walk_registers which is in the same module).

I'm not sure what the most appropriate return value would be, or what if this affects other areas as well.