mfd: Fix memory leak in mfd_add_devices()

If the first call to mfd_add_device() fails, no child devices have been
registered to the parent yet, and thus mfd_remove_devices() won't find
anything to remove nor free.
Hence the previously allocated array of atomic_t objects will leak.

Free the array instead of calling mfd_remove_devices() on failure during
the first loop iteration to fix this.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>