scsi: ufs: Avoid writing null to Boot LUN enable attribute

In ufshcd_query_ioctl(), if attribute value passed in
user buffer is null, boot feature will be disabled and
device enters in EDL mode.
To fix this, add check in ioctl path to avoid writing 00h
to Boot LUN enable attribute.

Change-Id: Ib7983075de3d6968a215cbc8b79c42a20fcc71a4
Signed-off-by: Sayali Lokhande <sayalil@codeaurora.org>