scsi: qedi: Fix SYSFS_FLAG_FW_SEL_BOOT formatting

The format used for formatting SYSFS_FLAG_FW_SEL_BOOT creates the
following warning:

drivers/scsi/qedi/qedi_main.c:2259:35: warning: format specifies type
'char' but the argument has type 'int' [-Wformat]
                   rc = snprintf(buf, 3, "%hhd\n",
SYSFS_FLAG_FW_SEL_BOOT);

Fix this to cast the constant as a char since the intention is to print it
via sysfs as a byte.

Link: https://lore.kernel.org/r/20211130203813.12138-2-f.fainelli@gmail.com
Reported-by: kernel test robot <lkp@intel.com>
Acked-by: Manish Rangankar <mrangankar@marvell.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>