staging: rtl8192u: Replace function rtl8192_rx_enable()

staging: rtl8192u: Replace function rtl8192_rx_enable()

Remove function rtl8192_rx_enable as all it does is call
rtl8192_rx_initiate.
Rename rtl8192_rx_initiate to rtl8192_rx_enable and change its type from
static to non-static to maintain compatibility with call sites of
rtl8192_rx_enable.
Issue found with Coccinelle.

Signed-off-by: Nishka Dasgupta <nishkadg.linux@gmail.com>
Link: https://lore.kernel.org/r/20190701091552.12696-1-nishkadg.linux@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>