usb: gadget: udc: renesas_usb3: lock for PN_ registers access

commit 940f538a100c84c6e72813e4ac88bd1753a86945 upstream.

This controller disallows to change the PIPE until reading/writing
a packet finishes. However. the previous code is not enough to hold
the lock in some functions. So, this patch fixes it.

Fixes: 746bfe63 ("usb: gadget: renesas_usb3: add support for Renesas USB3.0 peripheral controller")
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>