dm: core: fix signedness in debug messages

dm: core: fix signedness in debug messages

outp always point to an unsigned type in ofnode_read_u* functions but
the format specifier is currently always using signed type.

This is an issue since the signed type can only contain half of the
unsigned type values above 0.

However, this now breaks another usecase. Indeed,
ofnode_read_s32_default is actually passing an s32 but it'll be printed
as a u32 instead. But since the function is called u32, it makes more
sense to have it print an unsigned value.

This was discovered because arm,smc-id = <0x82000010>; on RK3588S is
above the max signed value and therefore would return a negative signed
decimal value instead of its proper unsigned one.

Fixes: fa12dfa08a7b ("dm: core: support reading a single indexed u64 value")
Fixes: 4bb7075c830c ("dm: core: support reading a single indexed u32 value")
Fixes: 7e5196c409f1 ("dm: core: Add ofnode function to read a 64-bit int")
Fixes: 9e51204527dc ("dm: core: Add operations on device tree references")
Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
Reviewed-by: Simon Glass <sjg@chromium.org>