x86/fpu: Update the outdated comment above fpstate_init_user()

fpu_init_fpstate_user() was removed in:

  commit 582b01b6ab ("x86/fpu: Remove old KVM FPU interface").

Update that comment to accurately reflect the current state regarding its
callers.

Signed-off-by: Chao Gao <chao.gao@intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20250324131931.2097905-1-chao.gao@intel.com

arch/x86/kernel/fpu/core.c

@@ -508,7 +508,7 @@ static inline void fpstate_init_fstate(struct fpstate *fpstate)
 /*
  * Used in two places:
  * 1) Early boot to setup init_fpstate for non XSAVE systems
- * 2) fpu_init_fpstate_user() which is invoked from KVM
+ * 2) fpu_alloc_guest_fpstate() which is invoked from KVM
  */
 void fpstate_init_user(struct fpstate *fpstate)
 {