scsi: gdth: increase the procfs event buffer size

We print a 256 byte event string into a buffer that is only 161
bytes long, this is clearly wrong:

drivers/scsi/gdth_proc.c: In function 'gdth_show_info':
drivers/scsi/gdth.c:3660:41: error: '%s' directive writing up to 255 bytes into a region of size between 141 and 150 [-Werror=format-overflow=]
             sprintf(buffer,"Adapter %d: %s\n",
                                         ^~
/git/arm-soc/drivers/scsi/gdth.c:3660:13: note: 'sprintf' output between 13 and 277 bytes into a destination of size 161
             sprintf(buffer,"Adapter %d: %s\n",
             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                 dvr->eu.async.ionode,dvr->event_string);
                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

gcc calculates that the worst case buffer size would be 277 bytes,
so we can use that.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>