ubi: Kconfig: Fix MTD_UBI selection dependency

Remove the ARCH_SUNXI dependency on selection of RBTREE.

Cc: Boris Brezillon <boris.brezillon@free-electrons.com>
Cc: Maxime Ripard <maxime.ripard@free-electrons.com>
Cc: Jagan Teki <jagan@openedev.com>
Signed-off-by: Karl Beldan <karl.beldan-ext@sagemcom.com>
Reviewed-by: Tom Rini <trini@konsulko.com>

drivers/mtd/ubi/Kconfig

@@ -3,7 +3,7 @@ menu "UBI support"
 config MTD_UBI
 	bool "Enable UBI - Unsorted block images"
 	select CRC32
-	select RBTREE if ARCH_SUNXI
+	select RBTREE
 	help
 	  UBI is a software layer above MTD layer which admits of LVM-like
 	  logical volumes on top of MTD devices, hides some complexities of