scsi: fas216: fix sense buffer initialization

While testing with the ARM specific memset() macro removed, I ran into a
compiler warning that shows an old bug:

drivers/scsi/arm/fas216.c: In function 'fas216_rq_sns_done':
drivers/scsi/arm/fas216.c:2014:40: error: argument to 'sizeof' in 'memset' call is the same expression as the destination; did you mean to provide an explicit length? [-Werror=sizeof-pointer-memaccess]

It turns out that the definition of the scsi_cmd structure changed back
in linux-2.6.25, so now we clear only four bytes (sizeof(pointer))
instead of 96 (SCSI_SENSE_BUFFERSIZE). I did not check whether we
actually need to initialize the buffer here, but it's clear that if we
do it, we should use the correct size.

Fixes: de25deb1 ("[SCSI] use dynamically allocated sense buffer")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>