memory: brcmstb: dpfe: fix type declaration of variable "ret"

In some functions, variable "ret" should be ssize_t, so we fix it.

Fixes: 2f330caf ("memory: brcmstb: Add driver for DPFE")
Signed-off-by: Markus Mayer <mmayer@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>