Patch from Tapani P?lli to fix a memory leak in X11_InitKeyboard

Patch uses XkbFreeKeyboard to free the memory returned by XkbGetMap.
Earlier implementation called XkbFreeClientMap which frees all the maps
but not data->xkb structure itself, XkbFreeKeyboard will free maps and
the structure.

src/video/x11/SDL_x11keyboard.c

@@ -484,7 +484,7 @@ X11_QuitKeyboard(_THIS)
 
 #if SDL_VIDEO_DRIVER_X11_HAS_XKBKEYCODETOKEYSYM
     if (data->xkb) {
-        X11_XkbFreeClientMap(data->xkb, 0, True);
+        X11_XkbFreeKeyboard(data->xkb, 0, True);
         data->xkb = NULL;
     }
 #endif

src/video/x11/SDL_x11sym.h

@@ -179,6 +179,7 @@ SDL_X11_SYM(Status,XkbGetState,(Display* a,unsigned int b,XkbStatePtr c),(a,b,c)
 SDL_X11_SYM(Status,XkbGetUpdatedMap,(Display* a,unsigned int b,XkbDescPtr c),(a,b,c),return)
 SDL_X11_SYM(XkbDescPtr,XkbGetMap,(Display* a,unsigned int b,unsigned int c),(a,b,c),return)
 SDL_X11_SYM(void,XkbFreeClientMap,(XkbDescPtr a,unsigned int b, Bool c),(a,b,c),)
+SDL_X11_SYM(void,XkbFreeKeyboard,(XkbDescPtr a,unsigned int b, Bool c),(a,b,c),)
 SDL_X11_SYM(BOOL,XkbSetDetectableAutoRepeat,(Display* a, BOOL b, BOOL* c),(a,b,c),return)
 #endif