btrfs-progs: bump to version 4.0

Switch SITE to use BR2_KERNEL_MIRROR as well.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/btrfs-progs/btrfs-progs.hash

@@ -1,2 +1,2 @@
 # From https://www.kernel.org/pub/linux/kernel/people/kdave/btrfs-progs/sha256sums.asc
-sha256	248862a7e7e06188bb495bbaa05d3e0e34628b61a10ef03234b3b00698ce88db	btrfs-progs-v3.19.1.tar.xz
+sha256	179cf1acc1b0061548b8f1d9cf973a8338bf96f192cecad99ecdace9ae065a1f	btrfs-progs-v4.0.tar.xz

package/btrfs-progs/btrfs-progs.mk

@@ -4,8 +4,8 @@
 #
 ################################################################################
 
-BTRFS_PROGS_VERSION = 3.19.1
-BTRFS_PROGS_SITE = https://www.kernel.org/pub/linux/kernel/people/kdave/btrfs-progs
+BTRFS_PROGS_VERSION = 4.0
+BTRFS_PROGS_SITE = $(BR2_KERNEL_MIRROR)/linux/kernel/people/kdave/btrfs-progs
 BTRFS_PROGS_SOURCE = btrfs-progs-v$(BTRFS_PROGS_VERSION).tar.xz
 BTRFS_PROGS_DEPENDENCIES = host-pkgconf acl attr e2fsprogs lzo util-linux zlib
 BTRFS_PROGS_CONF_OPTS = --disable-backtrace