gallivm: (trivial) don't try to use rcp when the division 1/x is integer

This would just crash. Noticed by accident while checking int divisions by zero
with a quickly hacked piglit test.

Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Jose Fonseca <jfonseca@vmware.com>

src/gallium/auxiliary/gallivm/lp_bld_arit.c

@@ -1073,7 +1073,7 @@ lp_build_div(struct lp_build_context *bld,
 
    if(a == bld->zero)
       return bld->zero;
-   if(a == bld->one)
+   if(a == bld->one && type.floating)
       return lp_build_rcp(bld, b);
    if(b == bld->zero)
       return bld->undef;