misc: atsha204a: fix i2c address readout from DTS

This patch replaces use fdtdec_get_addr with simpler dev_read_addr().
fdtdec_get_addr doesn't work properly on ZynqMP-based (64bit) system. Although
not confirmed, it could be related to the fact, that quoting the documentation,
"This variant hard-codes the number of cells used to represent the address and
size based on sizeof(fdt_addr_t) and sizeof(fdt_size_t)".

Signed-off-by: Adrian Fiergolski <adrian.fiergolski@fastree3d.com>
Reviewed-by: Marek Behún <marek.behun@nic.cz>