python-pillow: fix typo on tiff package dependency

Fixes:

  http://autobuild.buildroot.net/results/5ac12f08a366fc15ec138c900df0e5f62d0b70bc/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/python-pillow/python-pillow.mk

@@ -33,7 +33,7 @@ else
 PYTHON_PILLOW_BUILD_OPTS += --disable-jpeg2000
 endif
 
-ifeq ($(BR2_PACKAGE_ZLIB),y)
+ifeq ($(BR2_PACKAGE_TIFF),y)
 PYTHON_PILLOW_DEPENDENCIES += tiff
 PYTHON_PILLOW_BUILD_OPTS += --enable-tiff
 else