net: phy: call phy_error_precise() while holding the lock

Move the locking out of phy_error_precise() and to its only call site,
merging with the locked region that has already been taken.

Tested-by: Jijie Shao <shaojijie@huawei.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>