usb: musb: remove hand-crafted id handling

This replaced the handcrafted id handling by the PLATFORM_DEVID_AUTO
value which should do the same thing.

This patch probably also fixes ux500 because I did not find the "musbid"
variable to remove. And we close a tiny-unlikely race window becuase the
old code gave the id back before device was destroyed in the remove
case.

[ balbi@ti.com : fixed up two failed hunks when applying patch ]

Cc: B, Ravi <ravibabu@ti.com>
Cc: Santhapuri, Damodar <damodar.santhapuri@ti.com>
Cc: Mian Yousaf Kaukab <mian.yousaf.kaukab@stericsson.com>
Cc: Bob Liu <lliubbo@gmail.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>