net: phy: dp83867: Fix a never true comparison

The type of the return value of phy_read() and phy_read_mmd() is int.
Change the variable to not be unsigned so that we not get into an
unsigned compared against 0.

Signed-off-by: Haolin Li <li.haolin@qq.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>
1 file changed