drivers: usb: Mark function as static in usbsevseg.c

Mark function my_memlen() as static in misc/usbsevseg.c because it is
not used outside this file.

This eliminates the following warning in misc/usbsevseg.c:
drivers/usb/misc/usbsevseg.c:60:15: warning: no previous prototype for ‘my_memlen’ [-Wmissing-prototypes]
Signed-off-by: Rashika Kheria <rashika.kheria@gmail.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/misc/usbsevseg.c

@@ -57,7 +57,7 @@ struct usb_sevsegdev {
  * if str commands are used, we would assume the end of string
  * so mem commands are used.
  */
-inline size_t my_memlen(const char *buf, size_t count)
+static inline size_t my_memlen(const char *buf, size_t count)
 {
 	if (count > 0 && buf[count-1] == '\n')
 		return count - 1;