[media] of: reserved_mem: restore old behavior when no region is defined

Change return value back to -ENODEV when no region is defined for given
device. This restores old behavior of this function, as some drivers rely
on such error code.

Fixes: 59ce4039 ("of: reserved_mem: add support for using more than
       one region for given device")

Reported-by: Liviu Dudau <liviu.dudau@arm.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Reviewed-by: Liviu Dudau <Liviu.Dudau@arm.com>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Sumit Semwal <sumit.semwal@linaro.org>