usb: gadget: configfs: Make check_user_usb_string() static
"linux/usb/gadget_configfs.h" is only included in
"drivers/usb/gadget/configfs.c", so there is no need to declare a function
in the header file. it is only used in this .c file.
It's better to have it static.
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/958cb49dca1bff4254a3492c018efbf3b01918b4.1723323107.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>