staging: ks7010: rename identifier retval to ret

Function uses identifier 'retval' to hold the error return value. The
rest of the driver uses 'ret' for this purpose. Being uniform in the
choice of identifiers generally adds to the cleanliness of the code,
also it is arguably easier to follow the code if one name is used for
one task.

Rename identifier 'retval' to 'ret'.

Signed-off-by: Tobin C. Harding <me@tobin.cc>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>