mtd: docg3 fix missing bitreverse lib

Fix missing dependency which can cause a build error such
as: ERROR: "byte_rev_table" [drivers/mtd/devices/docg3.ko]
undefined!

Reported-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>