[POWERPC] Update MTFSF_L() comment

David Woodhouse points out that the comment accompanying the MTFSF_L
macro is misleading. We should make it clear that the L bit is ignored
on older CPUS, not the entire instruction.
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

include/asm-powerpc/reg.h

@@ -503,7 +503,7 @@
 
 /*
  * An mtfsf instruction with the L bit set. On CPUs that support this a
- * full 64bits of FPSCR is restored and on other CPUs it is ignored.
+ * full 64bits of FPSCR is restored and on other CPUs the L bit is ignored.
  *
  * Until binutils gets the new form of mtfsf, hardwire the instruction.
  */