After IRA changes, atomic version will use one more register, but
non-atomic still use 2 registers, however this testcase isn't testing for
atomic feature, so I decide change the testcase to always use COUNT++
to test.

ChangeLog

gcc/testsuite/

Kito Cheng  <kito.cheng@sifive.com>

	* gcc.target/riscv/interrupt-2.c: Update testcase and expected output.