qemu-keymap: Silence memory leak warning from Clang's sanitizer

qemu-keymap: Silence memory leak warning from Clang's sanitizer

When compiling QEMU with "--enable-sanitizers --enable-xkbcommon --cc=clang"
there is a memory leak warning when running qemu-keymap:

 $ ./qemu-keymap -f pc-bios/keymaps/de -l de

 =================================================================
 ==610321==ERROR: LeakSanitizer: detected memory leaks

 Direct leak of 136 byte(s) in 1 object(s) allocated from:
     #0 0x5642830d0820 in __interceptor_calloc.part.11 asan_malloc_linux.cpp.o
     #1 0x7f31873b8d2b in xkb_state_new (/lib64/libxkbcommon.so.0+0x1dd2b) (BuildId: dd32581e2248833243f3f646324ae9b98469f025)

 SUMMARY: AddressSanitizer: 136 byte(s) leaked in 1 allocation(s).

It can be silenced by properly releasing the "state" again
after it has been used.

Message-Id: <20230221122440.612281-1-thuth@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>