usb: phy: Rename "B-device session end SRP" OTG FSM input

In accordance with OTG and EH supplement, the correct name
of the FSM input is b_ssend_srp.

Signed-off-by: Anton Tikhomirov <av.tikhomirov@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>