uvol: call umount instead of using 'block umount'

Calling 'block umount' results in *all* devices listed in
/etc/config/fstab being unmounted.
Just call 'umount /dev/$devname' directly instead as that has the
desired effect.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

utils/uvol/files/lvm.sh

@@ -202,7 +202,7 @@ disactivatevol() {
 		*)
 			[ "$lv_active" = "active" ] || return 0
 			devname="$(getdev "$1")"
-			[ "$devname" ] && /sbin/block umount "$devname"
+			[ "$devname" ] && umount "/dev/$devname"
 			lvm_cmd lvchange -a n "$lv_full_name"
 			lvm_cmd lvchange -k y "$lv_full_name" || return $?
 			return 0

utils/uvol/files/ubi.sh

@@ -168,12 +168,12 @@ disactivatevol() {
 	vol_is_mode "$voldev" wo && return 22
 	vol_is_mode "$voldev" wp && return 16
 	if vol_is_mode "$voldev" ro; then
-		/sbin/block umount "ubiblock${voldev:3}"
+		grep -q "^/dev/ubiblock${voldev:3}" /proc/self/mounts && umount "/dev/ubiblock${voldev:3}"
 		ubiblock --remove "/dev/$voldev"
 		ubirename "/dev/$ubidev" "uvol-ro-$1" "uvol-rd-$1" || return $?
 		return 0
 	elif vol_is_mode "$voldev" rw; then
-		/sbin/block umount "$voldev"
+		umount "/dev/$voldev"
 		ubirename "/dev/$ubidev" "uvol-rw-$1" "uvol-wd-$1" || return $?
 		block_hotplug remove "$voldev"
 		return 0