x86/speculation: Remove the extra #ifdef around CALL_NOSPEC

Commit:

  010c4a4 ("x86/speculation: Simplify and make CALL_NOSPEC consistent")

added an #ifdef CONFIG_MITIGATION_RETPOLINE around the CALL_NOSPEC definition.
This is not required as this code is already under a larger #ifdef.

Remove the extra #ifdef, no functional change.

vmlinux size remains same before and after this change:

 CONFIG_MITIGATION_RETPOLINE=y:
      text       data        bss         dec        hex    filename
  25434752    7342290    2301212    35078254    217406e    vmlinux.before
  25434752    7342290    2301212    35078254    217406e    vmlinux.after

 # CONFIG_MITIGATION_RETPOLINE is not set:
      text       data        bss         dec        hex    filename
  22943094    6214994    1550152    30708240    1d49210    vmlinux.before
  22943094    6214994    1550152    30708240    1d49210    vmlinux.after

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Link: https://lore.kernel.org/r/20250320-call-nospec-extra-ifdef-v1-1-d9b084d24820@linux.intel.com

Author: pa1gupta

arch/x86/include/asm/nospec-branch.h

@@ -435,12 +435,8 @@ static inline void call_depth_return_thunk(void) {}
  * Inline asm uses the %V modifier which is only in newer GCC
  * which is ensured when CONFIG_MITIGATION_RETPOLINE is defined.
  */
-#ifdef CONFIG_MITIGATION_RETPOLINE
 #define CALL_NOSPEC	__CS_PREFIX("%V[thunk_target]")	\
 			"call __x86_indirect_thunk_%V[thunk_target]\n"
-#else
-#define CALL_NOSPEC	"call *%[thunk_target]\n"
-#endif
 
 # define THUNK_TARGET(addr) [thunk_target] "r" (addr)