usb: musb: Double buffering issues in host mode TX

Whenever an URB is programmed for transfer, the TXFIFO
is flushed. This results in valid packets of the
previous transfer to get flushed when double buffering
is enabled (The MUSB_TXCSR_FIFONOTEMPTY bit in TXCSR
is set indicating that a packet in the FIFO is yet to be sent)
For ex:- In Host mode Audio, noise is heard in the headset
when double buffering is enabled on the ISO endpoint.
The fifo flush is removed for double buffering case.
The fifo is now flushed only in cases of error or when
aborting a transfer.

Also, In Host MSC case, data toggle errors are seen when double
buffering is enabled on the bulk endpoint. Whenever an URB is
programmed for transfer, the data toggle is set manually
resulting in data toggle errors on the bus. Leave the data
toggle handling upto the hardware in the double buffering case.

Signed-off-by: supriya karanth <supriya.karanth@stericsson.com>
Signed-off-by: Praveena NADAHALLY <praveen.nadahally@stericsson.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Felipe Balbi <balbi@ti.com>