devres: move the size check from alloc_dr() into a separate function

We will perform the same size check in devm_krealloc(). Move the relevant
code into a separate helper.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Link: https://lore.kernel.org/r/20200629065008.27620-3-brgl@bgdev.pl


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>