memory: brcmstb: dpfe: initialize priv->dev

Add missing initialization of priv->dev. It is only used in an
emergency error message that is very unlikely to ever occur, which is
how this has remained unnoticed.

Signed-off-by: Markus Mayer <mmayer@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>