fs/squashfs: fix BR2_TARGET_ROOTFS_SQUASHFS_BS_8K

Fix typo BR2_TARGET_ROOTFS_SQUASHFS_BS_84K
-> BR2_TARGET_ROOTFS_SQUASHFS_BS_8K added by commit
555f8dfd6ef893463ce19d5ee242afd6b83cb450 and raising the following build
failure:

/nvmedata/autobuild/instance-0/output-1/host/bin/mksquashfs: -b invalid block size

Fixes:
 - http://autobuild.buildroot.org/results/927f070dfc1a800e57ca6619f062940641837db9

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

fs/squashfs/Config.in

@@ -46,7 +46,7 @@ endchoice
 config BR2_TARGET_ROOTFS_SQUASHFS_BS
 	string
 	default "4K" if BR2_TARGET_ROOTFS_SQUASHFS_BS_4K
-	default "8K" if BR2_TARGET_ROOTFS_SQUASHFS_BS_84K
+	default "8K" if BR2_TARGET_ROOTFS_SQUASHFS_BS_8K
 	default "16K" if BR2_TARGET_ROOTFS_SQUASHFS_BS_16K
 	default "32K" if BR2_TARGET_ROOTFS_SQUASHFS_BS_32K
 	default "64K" if BR2_TARGET_ROOTFS_SQUASHFS_BS_64K