Enable Btrfs kernel driver as built-in

Signed-off-by: Alexey Charkov <alchark@flipper.net>

Author: alchark

configs/minconfig-mainline

@@ -724,7 +724,7 @@ CONFIG_MUX_MMIO=m
 CONFIG_EXT4_FS=y
 CONFIG_EXT4_FS_POSIX_ACL=y
 CONFIG_EXT4_FS_SECURITY=y
-CONFIG_BTRFS_FS=m
+CONFIG_BTRFS_FS=y
 CONFIG_BTRFS_FS_POSIX_ACL=y
 CONFIG_FANOTIFY=y
 CONFIG_FANOTIFY_ACCESS_PERMISSIONS=y