Remove unnecessary cases from rank_one_type's switch

Remove unnecessary cases from rank_one_type's switch

We return INCOMPATIBLE_TYPE_BADNESS for all these type codes, so we might as
well just let them go to the default case.

Incidentally, this patch also makes this false positive error go away when
compiling with gcc (Ubuntu 7.3.0-27ubuntu1~18.04) 7.3.0, default compiler on
Ubuntu 18.04.

  CXX    gdbtypes.o
/home/smarchi/src/binutils-gdb/gdb/gdbtypes.c: In function ‘rank rank_one_type(type*, type*, value*)’:
/home/smarchi/src/binutils-gdb/gdb/gdbtypes.c:4259:1: error: control reaches end of non-void function [-Werror=return-type]
 }
 ^

gdb/ChangeLog:

	* gdbtypes.c (rank_one_type): Remove unnecessary cases from switch.