x86/jump_label: Mark arguments as const to satisfy asm constraints

x86/jump_label: Mark arguments as const to satisfy asm constraints

When compiling an external kernel module with `-O0` or `-O1`, the following
compile error may be reported:

    ./arch/x86/include/asm/jump_label.h:25:2: error: impossible constraint in ‘asm’
       25 |  asm_volatile_goto("1:"
          |  ^~~~~~~~~~~~~~~~~

It appears that these lower optimization levels prevent GCC from detecting
that the key/branch arguments can be treated as constants and used as
immediate operands. To work around this, explicitly add the `const` label.

Signed-off-by: Jason Gerecke <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Reviewed-by: Steven Rostedt (VMware) <[email protected]>
Acked-by: Josh Poimboeuf <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]