dt-bindings: spi: mxic: The interrupt property is not mandatory

dt-bindings: spi: mxic: The interrupt property is not mandatory

BugLink: https://bugs.launchpad.net/bugs/1969110
commit 90c204d3195a795f77f5bce767e311dd1c59ca17 upstream.

The interrupt property is not mandatory at all, this property should not
be part of the required properties list, so move it into the optional
properties list.

Fixes: 326e5c8d4a87 ("dt-binding: spi: Document Macronix controller bindings")
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/linux-mtd/20211216111654.238086-8-miquel.raynal@bootlin.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit b2b85196a31a245093e770eecb788f1be81f5b9b)
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>