[kservice] improve backtrace service in kernel (#8144)

Signed-off-by: Shell <smokewood@qq.com>

libcpu/arm/cortex-a/backtrace.c

@@ -530,7 +530,7 @@ void rt_unwind(struct rt_hw_exp_stack *regs, unsigned int pc_adj)
     unwind_backtrace(&e_regs, __exidx_start, __exidx_end);
 }
 
-void rt_backtrace(void)
+rt_err_t rt_backtrace(void)
 {
     struct rt_hw_exp_stack regs;
 
@@ -539,4 +539,5 @@ void rt_backtrace(void)
     asm volatile ("mov %0, lr":"=r"(regs.lr));
     asm volatile ("mov %0, pc":"=r"(regs.pc));
     rt_unwind(&regs, 8);
+    return RT_EOK;
 }

libcpu/arm/cortex-a/backtrace.h

@@ -76,7 +76,6 @@ int unwind_frame(struct stackframe *frame, const struct unwind_idx **origin_idx,
 void unwind_backtrace(struct pt_regs *regs, const struct unwind_idx exidx_start[], const struct unwind_idx exidx_end[]);
 
 void rt_unwind(struct rt_hw_exp_stack *regs, unsigned int pc_adj);
-void rt_backtrace(void);
 
 #endif	/* !__ASSEMBLY__ */