[PATCH] RISC-V: Skip shift-shift-7.c under -Og

At -Og the a << 1 is kept as a separate slliw instead of being folded
into the zero_extendsidi2_shifted sequence, so the "slli" regex matches
both slliw and slli and the scan-assembler-times "slli" 1 check fails.
Skip the test under -Og.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/shift-shift-7.c: Skip under -Og.