[AMDGPU] Remove outdated FIXME in comments [NFC]

This case has already been handled by D106449.

llvm/lib/Target/AMDGPU/SIInstrInfo.cpp

@@ -2555,12 +2555,6 @@ void SIInstrInfo::insertIndirectBranch(MachineBasicBlock &MBB,
   BuildMI(&MBB, DL, get(AMDGPU::S_SETPC_B64))
     .addReg(PCReg);
 
-  // FIXME: If spilling is necessary, this will fail because this scavenger has
-  // no emergency stack slots. It is non-trivial to spill in this situation,
-  // because the restore code needs to be specially placed after the
-  // jump. BranchRelaxation then needs to be made aware of the newly inserted
-  // block.
-  //
   // If a spill is needed for the pc register pair, we need to insert a spill
   // restore block right before the destination block, and insert a short branch
   // into the old destination block's fallthrough predecessor.