usb: host/sl811-hcd: fix sparse warning

this patch fixes following sparse warning:
sl811-hcd.c:1804:24: warning: symbol 'sl811h_driver' was not declared. Should it be static?

Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>