mtd: spi-nor: intel: provide a range for poll_timout

The overall poll time here is INTEL_SPI_TIMEOUT * 1000 which is
5000 * 1000 - so 5seconds and it is coded as a tight loop here delay_us
to readl_poll_timeout() is set to 0. As this is never called in an atomic
context sleeping should be no issue and there is no reasons for the
tight-loop here.

Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>