Fix "Could not resolve keysym" errors

Fix "Could not resolve keysym" errors

On many layouts, the following error appears:
Internal error:   Could not resolve keysym 10005b0
(Which is like the trademark of libxkbcommon now, and makes
unicode-heavy symbol files pretty useless).

This occurs when a keysym string (in this case, 10005b0) is passed to
xkb_string_to_keysym, but cannot be resolved.
This in turn happens because the parser passes on hexadecimal keysym
strings without the leading "0x", thus leaving the resolving function
without a way to disambiguate it as a number.

Therefore, make sure to pass on the "0x". The file symbols.c in xkbcomp
project does the same; it probably got lost in translation.

Signed-off-by: Ran Benita <ran234@gmail.com>