phy: twl4030-usb: Relase usb phy on unload

Otherwise rmmod omap2430; rmmod phy-twl4030-usb; modprobe omap2430
will try to use a non-existing phy and oops:

Unable to handle kernel paging request at virtual address b6f7c1f0
...
[<c048a284>] (devm_usb_get_phy_by_node) from [<bf0758ac>]
(omap2430_musb_init+0x44/0x2b4 [omap2430])
[<bf0758ac>] (omap2430_musb_init [omap2430]) from [<bf055ec0>]
(musb_init_controller+0x194/0x878 [musb_hdrc])

Cc: stable@vger.kernel.org
Cc: Bin Liu <b-liu@ti.com>
Cc: Felipe Balbi <balbi@ti.com>
Cc: Kishon Vijay Abraham I <kishon@ti.com>
Cc: NeilBrown <neil@brown.name>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>