thunderbolt: Make priority unsigned in struct tb_path

Clang warns:

drivers/thunderbolt/tunnel.c:504:17: warning: implicit truncation from
'int' to bit-field changes value from 5 to -3
[-Wbitfield-constant-conversion]
        path->priority = 5;
                       ^ ~
1 warning generated.

The priority member in struct tb_path is only ever assigned a positive
number:

$ rg -n priority drivers/thunderbolt/path.c
drivers/thunderbolt/tunnel.c:99:        path->priority = 3;
drivers/thunderbolt/tunnel.c:308:       path->priority = 2;
drivers/thunderbolt/tunnel.c:323:       path->priority = 1;
drivers/thunderbolt/tunnel.c:504:       path->priority = 5;

Furthermore, that value is only assigned to an unsigned integer in
tb_path_activate (the priority member in struct tb_regs_hop).

Fixes: 44242d6c ("thunderbolt: Add support for DMA tunnels")
Link: https://github.com/ClangBuiltLinux/linux/issues/454


Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>