mtd: spi-nor: Fix the disabling of write protection at init

spi_nor_spansion_clear_sr_bp() depends on spansion_quad_enable().
While spansion_quad_enable() is selected as default when
initializing the flash parameters, the nor->quad_enable() method
can be overwritten later on when parsing BFPT.

Select the write protection disable mechanism at spi_nor_init() time,
when the nor->quad_enable() method is already known.

Fixes: 191f5c2e ("mtd: spi-nor: use 16-bit WRR command when QE is set on spansion flashes")
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Reviewed-by: Vignesh Raghavendra <vigneshr@ti.com>
Signed-off-by: Richard Weinberger <richard@nod.at>