drivers: flash: spi_nor: fix few printf format warnings again

Looks like 9d5ebb3c introduced a new warning when building with
runtime sfdp on 32 bit platforms. Fix it for good by just casting the
operation to int and go back to use %u.

Tested with:

west build -p -b gd32f450z_eval samples/drivers/flash_shell \
	-DCONFIG_SPI_NOR_SFDP_RUNTIME=y
west build -p -b mpfs_icicle/polarfire/u54 samples/drivers/flash_shell

Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>