net: phy: sfp: Do not use "imply HWMON"

"imply HWMON" was supposed to ensure that the SFP phy code can be built
with HWMON enabled or disabled while at the same time ensuring that
HWMON is not built as module if SFP is built into the kernel.
Unfortunately, that does not work as intended. With "allmodconfig", it
results in several unrelated HWMON drivers to be disabled instead of
being built as module as expected.

Let's use the old "depends on HWMON || HWMON=n" instead. This is slightly
different (it enforces SFP to be built as module if HWMON is built as
module), but it is better than the alternative of using "IS_REACHABLE()"
in the driver since that would disable sensor support if HWMON is built
as module and SFP is built into the kernel.

Fixes: 1323061a ("net: phy: sfp: Add HWMON support for module sensors")
Cc: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>