mtd: spi-nor: intel: use true/false for boolean

writeable in struct intel_spi is a boolean and assignment should be to
true/false not 1/0 as recommended by boolinit.cocci.

Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Acked-by: Marek Vasut <marek.vasut@gmail.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Cyrille Pitchen <cyrille.pitchen@atmel.com>