ANDROID: block: Add support for small segments in blk_rq_map_user_iov()

Before changing the return value of bio_add_hw_page() into a value in
the range [0, len], make blk_rq_map_user_iov() fall back to copying data
if mapping the data is not possible due to the segment limit.

Bug: 261097222
Change-Id: Ia45812fd3c5ea2a125bfe5e3a8038c95981f4521
Signed-off-by: Bart Van Assche <bvanassche@google.com>