usb: phy: mxs: fix spelling mistake "stardard" -> "standard"

Trivial fix to spelling mistake in dev_dbg message

Acked-by: Peter Chen <peter.chen@nxp.com>
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>