crypto: crypto4xx - shuffle iomap in front of request_irq

It is possible to avoid the ce_base null pointer check in the
drivers' interrupt handler routine "crypto4xx_ce_interrupt_handler()"
by simply doing the iomap in front of the IRQ registration.

This way, the ce_base will always be valid in the handler and
a branch in an critical path can be avoided.

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>