[PATCH] mt76: Fix a signedness bug in mt7615_add_interface()

[Dan Carpenter]

The problem is that "mvif->omac_idx" is a u8 so it can't be negative
and the error handling won't work.  The get_omac_idx() function returns
-1 on error.

Fixes: 04b8e65922f6 ("mt76: add mac80211 driver for MT7615 PCIe-based chipsets")
Signed-off-by: Dan Carpenter <dan.carpen...@oracle.com>
---
 drivers/net/wireless/mediatek/mt76/mt7615/main.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wireless/mediatek/mt76/mt7615/main.c 
b/drivers/net/wireless/mediatek/mt76/mt7615/main.c
index 80e6b211f60b..8d7a47d1b205 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7615/main.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7615/main.c
@@ -77,11 +77,12 @@ static int mt7615_add_interface(struct ieee80211_hw *hw,
                goto out;
        }
 
-       mvif->omac_idx = get_omac_idx(vif->type, dev->omac_mask);
-       if (mvif->omac_idx < 0) {
+       idx = get_omac_idx(vif->type, dev->omac_mask);
+       if (idx < 0) {
                ret = -ENOSPC;
                goto out;
        }
+       mvif->omac_idx = idx;
 
        /* TODO: DBDC support. Use band 0 and wmm 0 for now */
        mvif->band_idx = 0;
-- 
2.18.0