MLK-9794-2 usb: common: otg: clear host_request_flag when leaves peripheral

This patch clear host_request_flag when leaves peripheral state, instead of
entering host state, this can make sure this flag can be cleared after try
to do role switch, no matter the role switch succeeds or not.

Acked-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Li Jun <b47624@freescale.com>