riscv: Fix spurious errors from __get/put_kernel_nofault

These macros did not initialize __kr_err, so they could fail even if
the access did not fault.

Cc: stable@vger.kernel.org
Fixes: d464118c ("riscv: implement __get_kernel_nofault and __put_user_nofault")
Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>
Link: https://lore.kernel.org/r/20240312022030.320789-1-samuel.holland@sifive.comSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/include/asm/uaccess.h

@@ -319,7 +319,7 @@ unsigned long __must_check clear_user(void __user *to, unsigned long n)
 
 #define __get_kernel_nofault(dst, src, type, err_label)			\
 do {									\
-	long __kr_err;							\
+	long __kr_err = 0;						\
 									\
 	__get_user_nocheck(*((type *)(dst)), (type *)(src), __kr_err);	\
 	if (unlikely(__kr_err))						\
@@ -328,7 +328,7 @@ do {									\
 
 #define __put_kernel_nofault(dst, src, type, err_label)			\
 do {									\
-	long __kr_err;							\
+	long __kr_err = 0;						\
 									\
 	__put_user_nocheck(*((type *)(src)), (type *)(dst), __kr_err);	\
 	if (unlikely(__kr_err))						\