mt76: mt7915: fix endianness warnings in mt7915_mac_tx_free()

Fix the following sparse warning in mt7915_mac_tx_free routine:
warning: incorrect type in assignment (different base types)
   expected unsigned int [usertype] *cur_info
   got restricted __le32 *
   warning: cast to restricted __le32

Fixes: c17780e7 ("mt76: mt7915: add txfree event v3")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>