staging: panel: return register value

we were returning success even if the module failed to register.
now we are returning the actual return value, success or error.

Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Acked-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>