mtd: m25p80: remove unnecessary ifdef

of_property_read_bool properly compiles away, no need to ifdef this
for non DT builds.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Marek Vasut <marex@denx.de>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>