block: Fix the setting of same_page variable

The same_page variable inside the function __bio_try_merge_page()
must be set to true if the merge happened within the same page.
As some the callers of this function take action based on that.

Change-Id: Iae4a7170aeaffcc0b9c424368c7d8127d51a177b
Fixes: 1bbb4bd9 ("block: disable multi-page bvec")
Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>