mtd: Use of_property_read_bool()

Use of_property_read_bool() to read boolean properties rather than
of_get_property(). This is part of a larger effort to remove callers
of of_get_property() and similar functions. of_get_property() leaks
the DT property data pointer which is a problem for dynamically
allocated nodes which may be freed.

Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20240731191312.1710417-22-robh@kernel.org