util/nvmutil: make rhex err_if consistent

n + 1 is the same as saying sizeof(rnum) in this case.
we should be clear about that, in code. n is irrelevant
here, since it is only an index for the return value.

Signed-off-by: Leah Rowe <leah@libreboot.org>

util/nvmutil/nvmutil.c

@@ -368,7 +368,8 @@ rhex(void)
 
 	if (!n) {
 		n = sizeof(rnum) - 1;
-		err_if(read(rfd, (uint8_t *) &rnum, n + 1) != sizeof(rnum));
+		err_if(read(rfd, (uint8_t *) &rnum, sizeof(rnum))
+		    != sizeof(rnum));
 	}
 
 	return rnum[n--] & 0xf;