Fixed clobbered output of the "help usb" command

The "usb help" doesn't format the output correctly:

=> help usb
usb - USB sub-system

Usage:
usb reset - reset (rescan) USB controller
usb stop [f]  - stop USB [f]=force stop
usb tree  - show USB device tree
usb info [dev] - show available USB devices
usb storage  - show details of USB storage devices
usb dev [dev] - show or set current USB storage device
usb part [dev] - print partition table of one or all USB storage devices
usb read addr blk# cnt - read `cnt' blocks starting at block `blk#'
    to memory address `addr'usb write addr blk# cnt - write `cnt'
blocks starting at block `blk#' from memory address `addr'
=>

With fix below applied, the output is correct:

=> help usb
usb - USB sub-system

Usage:
usb reset - reset (rescan) USB controller
usb stop [f]  - stop USB [f]=force stop
usb tree  - show USB device tree
usb info [dev] - show available USB devices
usb storage  - show details of USB storage devices
usb dev [dev] - show or set current USB storage device
usb part [dev] - print partition table of one or all USB storage devices
usb read addr blk# cnt - read `cnt' blocks starting at block `blk#'
    to memory address `addr'
usb write addr blk# cnt - write `cnt' blocks starting at block `blk#'
    from memory address `addr'
=>
Signed-off-by: NSergei Poselenov <sposelenov@emcraft.com>

common/cmd_usb.c

@@ -712,7 +712,7 @@ U_BOOT_CMD(
 	"usb part [dev] - print partition table of one or all USB storage"
 	" devices\n"
 	"usb read addr blk# cnt - read `cnt' blocks starting at block `blk#'\n"
-	"    to memory address `addr'"
+	"    to memory address `addr'\n"
 	"usb write addr blk# cnt - write `cnt' blocks starting at block `blk#'\n"
 	"    from memory address `addr'"
 );