testsuite: Fix up toplevel-asm-1.c for LoongArch

Like RISC-V, on LoongArch we don't really support %cN for SYMBOL_REFs
even with -fno-pic.

gcc/testsuite/ChangeLog:

	* c-c++-common/toplevel-asm-1.c: Use %cc3 %cc4 instead of %c3
	%c4 on LoongArch.