memory: brcmstb: dpfe: pass *priv as argument to brcmstb_dpfe_download_firmware()

Rather than passing a (struct platform_device *) to
brcmstb_dpfe_download_firmware(), we pass a (struct private_data *).
This is the more sensible thing to do.

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