usb: musb: dsps: remove declartion for dsps_musb_try_idle()

This patch moves dsps_musb_try_idle() before dsps_musb_enable() so the
declaration (of dsps_musb_try_idle() can be removed.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>