Staging: ramzswap: Remove redundant check for zero page

ramzswap_free_page() already handles the case for zero filled
pages. So, remove redundant logic for the same in ramzswap_write().

Signed-off-by: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>