staging: rtl8723bs: core: Remove function enable_rate_adaptive()

Remove function enable_rate_adaptive as all it does is call
Update_RA_Entry.
Modify the single callsite of enable_rate_adaptive to call
Update_RA_Entry directly instead.
Issue found with Coccinelle.

Signed-off-by: Nishka Dasgupta <nishkadg.linux@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>