[avr,committed]: Remove superfluous CLR of zero_reg.

[Georg-Johann Lay]

https://gcc.gnu.org/r238850

Applied this obvious change to __muldi3 which cleared zero_reg at the end of 
the function.  This is not needed because there was a call to __umulsidi3 which 
already cleared zero_reg.

Johann

libgcc/
	* config/avr/lib1funcs.S (__muldi3) [have MUL]: No need to clear
	zero_reg as previous call to __umulhisi3 already cleared it.

Index: config/avr/lib1funcs.S
===================================================================
--- config/avr/lib1funcs.S	(revision 238849)
+++ config/avr/lib1funcs.S	(working copy)
@@ -958,7 +958,6 @@ DEFUN __muldi3
      wmov    A4, C4
      wmov    A6, C6

-    clr     __zero_reg__
      pop     r16
      pop     r17
      pop     r28