remoteproc: k3: Fix NULL vs IS_ERR() bug in k3_reserved_mem_init()

remoteproc: k3: Fix NULL vs IS_ERR() bug in k3_reserved_mem_init()

The devm_ioremap_resource_wc() function never returns NULL, it returns
error pointers.  Update the error checking to match.

Fixes: 67a7bc7f0358 ("remoteproc: Use of_reserved_mem_region_* functions for "memory-region"")
Signed-off-by: Chen Ni <nichen@iscas.ac.cn>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20260227092110.4044313-1-nichen@iscas.ac.cn
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>