regmap: Introduce init_range

regmap: Introduce init_range

Both fdtdec_get_addr_size_fixed and of_address_to_resource can fail with
an error, which is not currently checked during regmap initialization.

Since the indentation depth is already quite deep, extract a new
'init_range' method to do the initialization.

Reviewed-by: Anatolij Gustschin <[email protected]>
Reviewed-by: Simon Glass <[email protected]>
Signed-off-by: Mario Six <[email protected]>