Staging: hv: storvsc: Fix a bug in create_bounce_buffer()

Set the length field of the scatter gather elements correctly when we create
the bounce buffer. When we use the bounce buffer for a "write" operation,
the act of copying to the bounce buffer, correctly deals with this issue.
However, on the "read" side, the current code was not correctly setting
the buffer length. Fix this bug. Note that when we copy from the bounce
buffer (for the read case), the amount we copy is controlled by the original
scatter gather list given to the driver.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Reported-by: Dadok Milan <dadok@kvados.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>