staging: rtl8192e: rename members of struct chnl_txpow_triple - style

Rename following members of chnl_txpow_triple to fix checkpatch
warning: Avoid CamelCase
	FirstChnl -> first_channel
	NumChnls -> num_channels
	MaxTxPowerInDbm -> max_tx_power

Signed-off-by: Himadri Pandya <himadri18.07@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>