dm: Fix build error when OF_CONTROL is not set

With OF_CONTROL disabled the build fails for
include/dm/read.h:932:10: error: ‘ENOTSUPP’ undeclared (first use in this function)
  932 |  return -ENOTSUPP;

Fixes: 45224e8f ("dm: core: gracefully handle alias seq without of")
Signed-off-by: Dan Murphy <dmurphy@ti.com>