mtd: spi-nor: micron-st: Remove status polling on volatile registers write

Writing volatile registers are instant according to Micron and do not
need any status polling. Remove status polling on volatile registers write.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Signed-off-by: Pratyush Yadav <p.yadav@ti.com>
Reviewed-by: Michael Walle <michael@walle.cc>
Link: https://lore.kernel.org/r/20220420103427.47867-12-tudor.ambarus@microchip.com