staging: rtl8723bs: Fix camel-case names in phy_get_tx_pwr_lmt().

Change camel-case names to snake-case names; to avoid variable name
conflicts, rename table index variables to idx_*.

Signed-off-by: Quytelda Kahja <quytelda@tamalin.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>