usb: imx21-hcd: Include missing linux/module.h

Include <linux/module.h>, so that the following errors are fixed:

drivers/usb/host/imx21-hcd.c:1929:20: error: expected declaration specifiers or '...' before string constant
drivers/usb/host/imx21-hcd.c:1930:15: error: expected declaration specifiers or '...' before string constant
drivers/usb/host/imx21-hcd.c:1931:16: error: expected declaration specifiers or '...' before string constant
drivers/usb/host/imx21-hcd.c:1932:14: error: expected declaration specifiers or '...' before string constant

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>