parisc: Makefile: fix a typo in palo.conf

Correct "objree" to "objtree". "objree" is not defined.

Fixes: 75dd4747 ("kbuild: remove src and obj from the top Makefile")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Cc: Helge Deller <deller@gmx.de>
Cc: linux-parisc@vger.kernel.org
Signed-off-by: Helge Deller <deller@gmx.de>
Cc: stable@vger.kernel.org # v5.3+