stb6100: fix buffer length check in stb6100_write_reg_range()

commit 7e6bd12f upstream.

We are checking sizeof() the wrong variable!

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
Cc: Willy Tarreau <w@1wt.eu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>