stm32l: set default padded value

The stm32l family has an erased value of 0x00, so overide the defaults used
by OpenOCD.

Change-Id: I314bdef1f8482fbcbd43e0f413247d3a35af869d
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/1636
Tested-by: jenkins

src/flash/nor/stm32f1x.c

@@ -150,6 +150,9 @@ FLASH_BANK_COMMAND_HANDLER(stm32x_flash_bank_command)
 	stm32x_info->register_base = FLASH_REG_BASE_B0;
 	stm32x_info->user_bank_size = bank->size;
 
+	/* the stm32l erased value is 0x00 */
+	bank->default_padded_value = 0x00;
+
 	return ERROR_OK;
 }