media: venus: firmware: Use of_reserved_mem_lookup()

Reserved memory can be either looked up using the generic function
of_address_to_resource() or using the special of_reserved_mem_lookup().
The latter has the advantage that it ensures that the referenced memory
region was really reserved and is not e.g. status = "disabled".

of_reserved_mem also supports allocating reserved memory dynamically at
boot time. This works only when using of_reserved_mem_lookup() since
there won't be a fixed address in the device tree.

Switch the code to use of_reserved_mem_lookup(). There is no functional
difference for static reserved memory allocations.

Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Signed-off-by: Stanimir Varbanov <stanimir.k.varbanov@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>