AVR: Rename test case to according PR number.

	PR rtl-optimization/PR117189
gcc/testsuite/
	* gcc.target/avr/torture/lra-pr116550-2.c: Rename to...
	* gcc.target/avr/torture/pr117189.c: ...this.

diff --git a/gcc/testsuite/gcc.target/avr/torture/lra-pr116550-2.c b/gcc/testsuite/gcc.target/avr/torture/pr117189.c
similarity index 100%
rename from gcc/testsuite/gcc.target/avr/torture/lra-pr116550-2.c
rename to gcc/testsuite/gcc.target/avr/torture/pr117189.c