wifi: rtl8xxxu: Rename some registers

Give proper names:

RF6052_REG_UNKNOWN_56 -> RF6052_REG_PAD_TXG
RF6052_REG_UNKNOWN_DF -> RF6052_REG_GAIN_CCA

And fix typos:

REG_OFDM0_AGCR_SSI_TABLE -> REG_OFDM0_AGC_RSSI_TABLE
REG_BB_ACCEESS_CTRL -> REG_BB_ACCESS_CTRL

Signed-off-by: Bitterblue Smith <rtl8821cerfe2@gmail.com>
Reviewed-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/40157253-76bd-8b23-06e0-3365139b5395@gmail.com