riscv: simplify longjmp

The value returned by setjmp must be nonzero. If zero is passed as
parameter it must be replaced by 1.

This patch reduces the code size a bit.

Signed-off-by: Heinrich Schuchardt <[e-mail]>
Reviewed-by: Sean Anderson <[e-mail]>
Reviewed-by: Leo Yu-Chi Liang <[e-mail]>

arch/riscv/lib/setjmp.S

···
 	LOAD_IDX(sp, 13)
 
 	/* Move the return value in place, but return 1 if passed 0. */
-	beq a1, zero, longjmp_1
-	mv a0, a1
-	ret
-
-	longjmp_1:
-	li a0, 1
+	seqz a0, a1
+	add a0, a0, a1
 	ret
 ENDPROC(longjmp)
 .popsection