Fix format-truncation compile failure by typecasting USB IDs (#8250)

This patch adds safe_atoux16 for parsing an unsigned hexadecimal 16bit int, and
uses that for parsing USB device and vendor IDs.

This fixes a compile error with gcc-8 because while we know that USB IDs are 2 bytes,
the compiler does not know that.

../src/udev/udev-builtin-hwdb.c:80:38: error: '%04X' directive output may be
truncated writing between 4 and 8 bytes into a region of size between 2 and 6
[-Werror=format-truncation=]

Signed-off-by: Adam Williamson <awilliam@redhat.com>
Signed-off-by: Patrick Uiterwijk <puiterwijk@redhat.com>

src/basic/parse-util.c

@@ -531,6 +531,30 @@ int safe_atoi16(const char *s, int16_t *ret) {
         return 0;
 }
 
+int safe_atoux16(const char *s, uint16_t *ret) {
+        char *x = NULL;
+        unsigned long l;
+
+        assert(s);
+        assert(ret);
+
+        s += strspn(s, WHITESPACE);
+
+        errno = 0;
+        l = strtoul(s, &x, 16);
+        if (errno > 0)
+                return -errno;
+        if (!x || x == s || *x != 0)
+                return -EINVAL;
+        if (s[0] == '-')
+                return -ERANGE;
+        if ((unsigned long) (uint16_t) l != l)
+                return -ERANGE;
+
+        *ret = (uint16_t) l;
+        return 0;
+}
+
 int safe_atod(const char *s, double *ret_d) {
         _cleanup_(freelocalep) locale_t loc = (locale_t) 0;
         char *x = NULL;