riscv: Fix fp alignment bug in perf_callchain_user()

The standard RISC-V calling convention said:
	"The stack grows downward and the stack pointer is always
	kept 16-byte aligned".

So perf_callchain_user() should check whether 16-byte aligned for fp.

Link: https://riscv.org/wp-content/uploads/2015/01/riscv-calling.pdf

Fixes: dbeb90b0 ("riscv: Add perf callchain support")
Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Cc: Björn Töpel <bjorn@kernel.org>
Link: https://lore.kernel.org/r/20240708032847.2998158-2-ruanjinjie@huawei.comSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/kernel/perf_callchain.c

@@ -62,7 +62,7 @@ void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
 	perf_callchain_store(entry, regs->epc);
 
 	fp = user_backtrace(entry, fp, regs->ra);
-	while (fp && !(fp & 0x3) && entry->nr < entry->max_stack)
+	while (fp && !(fp & 0x7) && entry->nr < entry->max_stack)
 		fp = user_backtrace(entry, fp, 0);
 }