ASoC: sirf: Fix potential NULL pointer dereference

There is a potential execution path in which function
platform_get_resource() returns NULL. If this happens,
we will end up having a NULL pointer dereference.

Fix this by replacing devm_ioremap with devm_ioremap_resource,
which has the NULL check and the memory region request.

This code was detected with the help of Coccinelle.

Cc: stable@vger.kernel.org
Fixes: 2bd8d1d5 ("ASoC: sirf: Add audio usp interface driver")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Mark Brown <broonie@kernel.org>