buildroot

package/python-pillow: fix wrong install step

This patch changes PYTHON_PILLOW_INSTALL_TARGET_CMDS to actually
install pillow in target directory instead of host.

While at it, it also fixes the version for the hash, and uses the more
conventional "define ... endef" construct to define variables in
python-pillow.mk.

Signed-off-by: Angelo Compagnucci <angelo.compagnucci@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>