Currently pointer phy0 is being dereferenced via the assignment of
phy on the call to phy_get_drvdata before phy0 is null checked, this
can lead to a null pointer dereference. Fix this by performing the
null check on phy0 before the call to phy_get_drvdata. Also replace
the phy0 == NULL check with the more usual !phy0 idiom.

Addresses-Coverity: ("Dereference before null check")
Fixes: e6f32efb ("phy: sun4i-usb: Make sure to disable PHY0 passby for peripheral mode")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/20200625124428.83564-1-colin.king@canonical.comSigned-off-by: Vinod Koul <vkoul@kernel.org>