libbpf: Fix syscall access arguments on riscv

Since commit 08d0ce30 ("riscv: Implement syscall wrappers"), riscv
selects ARCH_HAS_SYSCALL_WRAPPER so let's use the generic implementation
of PT_REGS_SYSCALL_REGS().

Fixes: 08d0ce30 ("riscv: Implement syscall wrappers")
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Link: https://lore.kernel.org/bpf/20231004110905.49024-2-bjorn@kernel.org

tools/lib/bpf/bpf_tracing.h

@@ -362,8 +362,6 @@ struct pt_regs___arm64 {
 #define __PT_PARM7_REG a6
 #define __PT_PARM8_REG a7
 
-/* riscv does not select ARCH_HAS_SYSCALL_WRAPPER. */
-#define PT_REGS_SYSCALL_REGS(ctx) ctx
 #define __PT_PARM1_SYSCALL_REG __PT_PARM1_REG
 #define __PT_PARM2_SYSCALL_REG __PT_PARM2_REG
 #define __PT_PARM3_SYSCALL_REG __PT_PARM3_REG