Fix typo in mt7915_muru_debug_set routine and pass muru_debug value to
mt7915_mcu_muru_debug_set() instead of data pointer.

Fixes: 1966a507 ("mt76: mt7915: add mu-mimo and ofdma debugfs knobs")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>