Fix generate-keynames.sh script for cross-compilation

generate-keynames.sh reads /usr/include/linux to find the keyname
symbols. However, when cross-compiling, the include path points
somewhere else. Allow the user to pass CROSS_ROOT to point to the
root of the cross-compilation environment.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
---
diff -rup dvb-apps-83c746462ccb.orig/util/av7110_loadkeys/generate-keynames.sh dvb-apps-83c746462ccb/util/av7110_loadkeys/generate-keynames.sh
--- dvb-apps-83c746462ccb.orig/util/av7110_loadkeys/generate-keynames.sh	2012-12-06 10:38:07.000000000 +0100
+++ dvb-apps-83c746462ccb/util/av7110_loadkeys/generate-keynames.sh	2013-08-29 21:47:09.717991439 +0200
@@ -18,7 +18,7 @@ echo "};" >> $1
 echo >> $1
 echo >> $1
 echo "static struct input_key_name key_name [] = {" >> $1
-for x in $(cat /usr/include/linux/input.h input_fake.h | \
+for x in $(cat ${CROSS_ROOT}/usr/include/linux/input.h input_fake.h | \
            egrep "#define[ \t]+KEY_" | grep -v KEY_MAX | \
            cut -f 1 | cut -f 2 -d " " | sort -u) ; do
     echo "        { \"$(echo $x | cut -b 5-)\", $x }," >> $1
@@ -26,7 +26,7 @@ done
 echo "};" >> $1
 echo >> $1
 echo "static struct input_key_name btn_name [] = {" >> $1
-for x in $(cat /usr/include/linux/input.h input_fake.h | \
+for x in $(cat ${CROSS_ROOT}/usr/include/linux/input.h input_fake.h | \
            egrep "#define[ \t]+BTN_" | \
            cut -f 1 | cut -f 2 -d " " | sort -u) ; do
      echo "        { \"$(echo $x | cut -b 5-)\", $x }," >> $1