basic_mmio_gpio: request register regions

Make sure that we get the register regions with request_mem_region()
before ioremap() to make sure we have exclusive access.

Signed-off-by: Jamie Iles <jamie@jamieiles.com>
Acked-by: Anton Vorontsov <cbouatmailru@gmail.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>