phy: ti: gmii-sel: Add a sanity check on the phy_id

phy: ti: gmii-sel: Add a sanity check on the phy_id

The "phy_id" comes from the device tree so it's going to be correct.
But static checkers sometimes complain when we have an upper bounds
check with no lower bounds check.  Also it's a bit unusual that the
lowest valid number is 1 instead of 0 so adding a check could
potentially help someone.

Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patch.msgid.link/aPJpB-QI8FMpFGOk@stanley.mountain
Signed-off-by: Vinod Koul <vkoul@kernel.org>