target-arm: Fix typo

The command line option is called -kernel, not -kenrel.

Cc: Paul Brook <paul@codesourcery.com>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NAndreas Färber <andreas.faerber@web.de>
Signed-off-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>

target-arm/helper.c

@@ -298,7 +298,7 @@ void cpu_reset(CPUARMState *env)
         if (rom) {
             /* We should really use ldl_phys here, in case the guest
                modified flash and reset itself.  However images
-               loaded via -kenrel have not been copied yet, so load the
+               loaded via -kernel have not been copied yet, so load the
                values directly from there.  */
             env->regs[13] = ldl_p(rom);
             pc = ldl_p(rom + 4);