misc: sram: Generate unique names for subpools

The current code will, if we do not specify unique labels
for the SRAM subnodes, fail to register several nodes named
the same.

Example:

sram@40020000 {
  (...)
  sram@0 {
    (...)
  };
  sram@1000 {
    (...)
  };
};

Since the child->name in both cases will be "sram" the
gen_pool_create() will fail because the name is not unique.

Use dev_name() for the device as this will have bus ID
set to the fully translated address for the node, and that
will always be unique.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20230417-ux500-sram-v2-2-6e62ad551faa@linaro.org