package/git: fix build with iconv

Our libiconv shouldn't need the ICONV_OMITS_BOM workaround.

We also need to correctly set the iconv path so that we don't use the
host iconv path.

Fixes:
 - http://autobuild.buildroot.net/results/027/027602a750fd0989f9861773a2c4672667590acc

Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

package/git/git.mk

@@ -49,7 +49,8 @@ endif
 ifeq ($(BR2_PACKAGE_LIBICONV),y)
 GIT_DEPENDENCIES += libiconv
 GIT_CONF_ENV_LIBS += -liconv
-GIT_CONF_OPTS += --with-iconv=/usr/lib
+GIT_CONF_OPTS += --with-iconv=$(STAGING_DIR)/usr
+GIT_CONF_ENV += ac_cv_iconv_omits_bom=no
 else
 GIT_CONF_OPTS += --without-iconv
 endif