x86: fix return value checks of set_guest_{machinecheck,nmi}_trapbounce

x86: fix return value checks of set_guest_{machinecheck,nmi}_trapbounce

Commit 0142064421 ("x86/traps: move set_guest_{machine,nmi}_trapbounce")
converted the functions' return types from int to bool without also
correcting the checks in assembly code: The ABI does not guarantee sub-
32-bit return values to be promoted to 32 bits.

Take the liberty and also adjust the number of spaces used in the compat
code, such that both code sequences end up similar (they already are in
the non-compat case).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Release-acked-by: Juergen Gross <jgross@suse.com>