of: dynamic: Constify parameter in of_changeset_add_prop_string_array()

of: dynamic: Constify parameter in of_changeset_add_prop_string_array()

The str_array parameter has no reason to be an un-const array.
Indeed, elements of the 'str_array' array are not changed by the code.

Constify the 'str_array' array parameter.
With this const qualifier added, the following construction is allowed:
  static const char * const tab_str[] = { "string1", "string2" };
  of_changeset_add_prop_string_array(..., tab_str, ARRAY_SIZE(tab_str));

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Link: https://lore.kernel.org/r/20240527161450.326615-14-herve.codina@bootlin.com
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>