riscv:fix user_regs_struct macro issue
riscv:fix user_regs_struct macro issue

Fix #4110 . With this patch, running tools/cachestat on riscv64 can
get the expected result.

Signed-off-by: Mingzheng Xing <0583e4621558ade9df3b17c061a0c1717051f54c@iscas.ac.cn>

iovisor/bcc,iovisor/bcc,iovisor/bcc,iovisor/bcc,iovisor/bcc