mt76: mt7921: remove incorrect error handling

Clang points out a mistake in the error handling in
mt7921_mcu_tx_rate_report(), which tries to dereference a pointer that
cannot be initialized because of the error that is being handled:

drivers/net/wireless/mediatek/mt76/mt7921/mcu.c:409:3: warning: variable 'stats' is uninitialized when used here [-Wuninitialized]
                stats->tx_rate = rate;
                ^~~~~
drivers/net/wireless/mediatek/mt76/mt7921/mcu.c:401:32: note: initialize the variable 'stats' to silence this warning
        struct mt7921_sta_stats *stats;
                                      ^
Just remove the obviously incorrect line.

Fixes: 1c099ab4

 ("mt76: mt7921: add MCU support")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210225145953.404859-2-arnd@kernel.org