scsi: esas2r: Remove redundant NULL check on buffer

Buffer is a pointer to the static char array event_buffer and therefore
can never be null, so the check is redundant. Remove it.

Detected by CoverityScan, CID#1077556 ("Logically Dead Code")

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Bradley Grove <bgrove@attotech.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>