staging: rtl8723bs: hal: Replace function PHY_SetTxPowerIndex()

Remove function PHY_SetTxPowerIndex as it does nothing except call
PHY_SetTxPowerIndex_8723B.
Rename PHY_SetTxPowerIndex_8723B to PHY_SetTxPowerIndex to maintain
compatibility with call site.
Issue found with Coccinelle.

Signed-off-by: Nishka Dasgupta <nishkadg.linux@gmail.com>
Link: https://lore.kernel.org/r/20190725052645.2372-2-nishkadg.linux@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>