mtd: spi-nor: Use dev_dbg insted of dev_err for low level info

mtd: spi-nor: Use dev_dbg insted of dev_err for low level info

What most users care about is "my dev is not working properly".
All low level information should be discovered when activating
the debug traces.

Keep error messages just for the following cases:
- when the SR/FSR report program or erase fails, or attempts of
  modifying a protected sector,
- when the JEDEC ID is not recognized,
- when the resume() call fails,
- when the spi_nor_check() fails.

Suggested-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Reviewed-by: Vignesh Raghavendra <vigneshr@ti.com>