remoteproc: k3-dsp: Fix return value check in k3_dsp_rproc_of_get_memories()

remoteproc: k3-dsp: Fix return value check in k3_dsp_rproc_of_get_memories()

In case of error, the function devm_ioremap_wc() returns NULL pointer
not ERR_PTR(). The IS_ERR() test in the return value check should be
replaced with NULL test.

Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Fixes: 6edbe024ba17 ("remoteproc: k3-dsp: Add a remoteproc driver of K3 C66x DSPs")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Acked-by: Suman Anna <s-anna@ti.com>
Link: https://lore.kernel.org/r/20200905122503.17352-1-yuehaibing@huawei.com
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>