firmware_loader: change enum fw_opt to u32

"enum fw_opt" is not used as an enum.
Change fw_opt to u32 as FW_OPT_* values are OR'd together.

Signed-off-by: Scott Branden <scott.branden@broadcom.com>
Acked-by: Luis Chamberlain <mcgrof@kernel.org>
Link: https://lore.kernel.org/r/20200522231202.13681-1-scott.branden@broadcom.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>