remoteproc: imx_rproc: Skip over memory region when node value is NULL

remoteproc: imx_rproc: Skip over memory region when node value is NULL

In imx_rproc_addr_init() "nph = of_count_phandle_with_args()" just counts
number of phandles. But phandles may be empty. So of_parse_phandle() in
the parsing loop (0 < a < nph) may return NULL which is later dereferenced.
Adjust this issue by adding NULL-return check.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: a0ff4aa6f010 ("remoteproc: imx_rproc: add a NXP/Freescale imx_rproc driver")
Signed-off-by: Aleksandr Mishin <amishin@t-argos.ru>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20240606075204.12354-1-amishin@t-argos.ru
[Fixed title to fit within the prescribed 70-75 charcters]
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>