serial: s5p: Use dev_read_addr_ptr() to get base address

serial: s5p: Use dev_read_addr_ptr() to get base address

As the address read from device tree is being cast to a pointer, it's
better to use dev_read_addr_ptr() API for getting that address. The more
detailed explanation can be found in commit a12a73b66476 ("drivers: use
dev_read_addr_ptr when cast to pointer").

Signed-off-by: Sam Protsenko <[email protected]>
Reviewed-by: Simon Glass <[email protected]>
Signed-off-by: Minkyu Kang <[email protected]>