m68k: fix command-line parsing when passed from u-boot

This patch fixes command_line array zero-terminated
one byte over the end of the array, causing boot to hang.
Signed-off-by: Angelo Dureghello <angelo@sysam.it>
Signed-off-by: Greg Ungerer <gerg@linux-m68k.org>

arch/m68k/kernel/uboot.c

@@ -102,5 +102,5 @@ __init void process_uboot_commandline(char *commandp, int size)
 	}
 
 	parse_uboot_commandline(commandp, len);
-	commandp[size - 1] = 0;
+	commandp[len - 1] = 0;
 }