[SCSI] sd: Fix parsing of 'temporary ' cache mode prefix

Commit 39c60a09 '[SCSI] sd: fix array cache flushing bug causing
performance problems' added temp as a pointer to "temporary " and used
sizeof(temp) - 1 as its length.  But sizeof(temp) is the size of the
pointer, not the size of the string constant.  Change temp to a static
array so that sizeof() does what was intended.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: stable@vger.kernel.org
Signed-off-by: James Bottomley <JBottomley@Parallels.com>