am7xxx-modeswitch: fix the Length field in the switch command

am7xxx-modeswitch: fix the Length field in the switch command

The switch_command is a USB storage message, the bulk_cb_wrap structure
from include/linux/usb/storage.h in the Linux kernel shows the fields
meanings:

struct bulk_cb_wrap {
	__le32	Signature;		/* contains 'USBC' */
	__u32	Tag;			/* unique per command id */
	__le32	DataTransferLength;	/* size of data */
	__u8	Flags;			/* direction in bit 0 */
	__u8	Lun;			/* LUN normally 0 */
	__u8	Length;			/* length of the CDB */
	__u8	CDB[16];		/* max command */
};

In switch_command the data in CDB is 16 bytes long (0x10), so using 0x0c
was wrong, it worked on some devices but it did not on others.

Use the correct value.

Thanks-to: Balasubramanian S <sbala214@gmail.com>