Fixes bug clearing the bss section for i386

Hi,
There is a bug in the code of clearing the bss section for processor
i386.(File: cpu/i386/start.S)
In the code, bss_start addr (starting addr of bss section) is put into
the register %eax, but the code which clears the bss section refers to
the addr pointed by %edi.

This patch fixes this bug by putting bss_start into %edi register.

Signed-off-by: Mushtaq Khan <mushtaq_k@procsys.com>

cpu/i386/start.S

@@ -149,7 +149,7 @@ data_ok:
 .progress3:
 
 	/* clear bss section in ram, size must be 4-byte aligned  */
-	movl	$_i386boot_bss_start, %eax        /* BSS start */
+	movl	$_i386boot_bss_start, %edi        /* MK_CHG BSS start */
 	movl	$_i386boot_bss_size, %ecx         /* BSS size */
 	movl	%ecx, %eax
 	andl	$3, %eax