staging/rtl8192e: Erroneous return codes (types and values)

This function returns a bool, that is supposed to be false when something
goes wrong. It's assumed this way by its lone calling function (which is
SetRFPowerState8190(), line 1445 of rtl8192e/rtl8192e/r8192E_phy.c)

Despite of this, this procedure returns non-null enumerations values or
negative codes instead. This patch fixes this.

Signed-off-by: Dominique van den Broeck <domdevlin@free.fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>