powerpc/xmon: Remove unused variable in xmon.c

Gets rid of this warning:

arch/powerpc/xmon/xmon.c: In function 'dump_log_buf':
arch/powerpc/xmon/xmon.c:2133: warning: unused variable 'i'
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/xmon/xmon.c

@@ -2130,7 +2130,7 @@ void
 dump_log_buf(void)
 {
         const unsigned long size = 128;
-        unsigned long i, end, addr;
+        unsigned long end, addr;
         unsigned char buf[size + 1];
 
         addr = 0;