net: usb: asix_devices: Fix PHY address mask in MDIO bus initialization

Syzbot reported shift-out-of-bounds exception on MDIO bus initialization.

The PHY address should be masked to 5 bits (0-31). Without this
mask, invalid PHY addresses could be used, potentially causing issues
with MDIO bus operations.

Fix this by masking the PHY address with 0x1f (31 decimal) to ensure
it stays within the valid range.

Fixes: 4faff709 ("net: usb: asix_devices: add phy_mask for ax88772 mdio bus")
Reported-by:  <syzbot+20537064367a0f98d597@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=20537064367a0f98d597


Tested-by:  <syzbot+20537064367a0f98d597@syzkaller.appspotmail.com>
Signed-off-by: Yuichiro Tsuji <yuichtsu@amazon.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20250818084541.1958-1-yuichtsu@amazon.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>