x86/irq: Fix comment on IRQ vector layout

commit f5a3562e ("x86/irq: Reserve a per CPU IDT vector for posted
MSIs") changed the first system vector from LOCAL_TIMER_VECTOR to
POSTED_MSI_NOTIFICATION_VECTOR. Reflect this change in the vector layout
comment as well.

However, instead of pointing to the specific vector, use the
FIRST_SYSTEM_VECTOR indirection which essentially refers to the same.

This avoids unnecessary modifications to the same comment whenever
additional system vectors get added.
Signed-off-by: Sohil Mehta <sohil.mehta@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Link: https://lore.kernel.org/all/20240812214318.2715360-1-sohil.mehta@intel.com

arch/x86/include/asm/irq_vectors.h

@@ -18,8 +18,8 @@
  *  Vectors   0 ...  31 : system traps and exceptions - hardcoded events
  *  Vectors  32 ... 127 : device interrupts
  *  Vector  128         : legacy int80 syscall interface
- *  Vectors 129 ... LOCAL_TIMER_VECTOR-1
- *  Vectors LOCAL_TIMER_VECTOR ... 255 : special interrupts
+ *  Vectors 129 ... FIRST_SYSTEM_VECTOR-1 : device interrupts
+ *  Vectors FIRST_SYSTEM_VECTOR ... 255   : special interrupts
  *
  * 64-bit x86 has per CPU IDT tables, 32-bit has one shared IDT table.
  *