mt76: mt7915: fix some sparse warnings

drivers/net/wireless/mediatek/mt76/mt7915/main.c:694:1: sparse:
sparse: context imbalance in 'mt7915_sta_rc_update' - wrong count at exit
drivers/net/wireless/mediatek/mt76/mt7915/mac.c:303:43: sparse: sparse: cast to restricted __le32
drivers/net/wireless/mediatek/mt76/mt7915/mac.c:304:43: sparse: sparse: cast to restricted __le32
drivers/net/wireless/mediatek/mt76/mt7915/mac.c:305:43: sparse: sparse: cast to restricted __le32
drivers/net/wireless/mediatek/mt76/mt7915/mac.c:319:35: sparse: sparse: cast to restricted __le32
drivers/net/wireless/mediatek/mt76/mt7915/mac.c:327:35: sparse: sparse: cast to restricted __le32
drivers/net/wireless/mediatek/mt76/mt7915/mac.c:345:41: sparse: sparse: cast to restricted __le32
drivers/net/wireless/mediatek/mt76/mt7915/mac.c:355:33: sparse: sparse: cast to restricted __le32
drivers/net/wireless/mediatek/mt76/mt7915/mac.c:451:21: sparse: sparse: invalid assignment: |=
drivers/net/wireless/mediatek/mt76/mt7915/mac.c:451:21: sparse:    left side has type unsigned int
drivers/net/wireless/mediatek/mt76/mt7915/mac.c:451:21: sparse:    right side has type restricted __le32

Fixes: e57b7901 ("mt76: add mac80211 driver for MT7915 PCIe-based chipsets")
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>