btrfs-progs: adjust install-static patch to install headers under $(prefix)/include/btrfs

Fixes:
http://autobuild.buildroot.net/results/15cc6523a42bf66508b2b37fd1fcb74625561ec2/

btrfs-progs 'make install' installs headers under $(prefix)/include/btrfs,
but our patch to also install headers for 'install-static' installed
directly into $(prefix)/include, confusing other packages as btrfs-progs
headers have very common names such as version, sizes.h, list.h, ioctl.h, ..

Fix it by adjusting the patch to also install under $(prefix)/include/btrfs.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit 83b40e1ea2e3ce046d7db442b01c3bfe52886ce8)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/btrfs-progs/0001-Makefile-install-static-library-and-headers-in-insta.patch

@@ -41,8 +41,8 @@ index 67fbc48..d9e34be 100644
  	$(LN_S) -f btrfs.static $(DESTDIR)$(bindir)/btrfsck.static
 +	$(INSTALL) -m755 -d $(DESTDIR)$(libdir)
 +	$(INSTALL) $(libs_static) $(DESTDIR)$(libdir)
-+	$(INSTALL) -m755 -d $(DESTDIR)$(incdir)
-+	$(INSTALL) -m644 $(libbtrfs_headers) $(DESTDIR)$(incdir)
++	$(INSTALL) -m755 -d $(DESTDIR)$(incdir)/btrfs
++	$(INSTALL) -m644 $(libbtrfs_headers) $(DESTDIR)$(incdir)/btrfs
  
  $(INSTALLDIRS):
  	@echo "Making install in $(patsubst install-%,%,$@)"