package/openjdk: set PATH before calling make

package/openjdk: set PATH before calling make

PATH must be set to $(BR_PATH) thanks to $(TARGET_MAKE_ENV) before
calling make otherwise build fails on:
/bin/bash: gawk: command not found

When build fails, config.log contains the following line:

configure:13709: checking for gawk
configure:13725: found /home/buildroot/autobuild/run/instance-3/output/host/bin/gawk
configure:13736: result: gawk
[...]
ac_cv_prog_AWK=gawk

Fixes:
 - http://autobuild.buildroot.org/results/43c5d08f599e8f44b59a576d243ae1c7b27de7a3

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>