x86/build: Don't verify mtools configuration file for isoimage

If mtools.conf is not generated before, 'make isoimage' could complain:

  Kernel: arch/x86/boot/bzImage is ready  (#597)
    GENIMAGE arch/x86/boot/image.iso
   *** Missing file: arch/x86/boot/mtools.conf
  arch/x86/boot/Makefile:144: recipe for target 'isoimage' failed

mtools.conf is not used for isoimage generation, so do not check it.
Signed-off-by: Changbin Du <changbin.du@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 4366d57a ("x86/build: Factor out fdimage/isoimage generation commands to standalone script")
Link: http://lkml.kernel.org/r/1512053480-8083-1-git-send-email-changbin.du@intel.comSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/boot/genimage.sh

@@ -44,9 +44,9 @@ FDINITRD=$6
 
 # Make sure the files actually exist
 verify "$FBZIMAGE"
-verify "$MTOOLSRC"
 
 genbzdisk() {
+	verify "$MTOOLSRC"
 	mformat a:
 	syslinux $FIMAGE
 	echo "$KCMDLINE" | mcopy - a:syslinux.cfg
@@ -57,6 +57,7 @@ genbzdisk() {
 }
 
 genfdimage144() {
+	verify "$MTOOLSRC"
 	dd if=/dev/zero of=$FIMAGE bs=1024 count=1440 2> /dev/null
 	mformat v:
 	syslinux $FIMAGE
@@ -68,6 +69,7 @@ genfdimage144() {
 }
 
 genfdimage288() {
+	verify "$MTOOLSRC"
 	dd if=/dev/zero of=$FIMAGE bs=1024 count=2880 2> /dev/null
 	mformat w:
 	syslinux $FIMAGE