mm/alloc: remove all unnecessary cast for alloc

Fix the minor style issue and remove unnecessary cast

Signed-off-by: chao an <anchao@xiaomi.com>

graphics/nxbe/nxbe_colormap.c

@@ -69,7 +69,7 @@ int nxbe_colormap(FAR NX_DRIVERTYPE *dev)
    */
 
   size  = 3 * CONFIG_NX_NCOLORS * sizeof(uint8_t);
-  alloc = (FAR uint8_t *)kmm_malloc(size);
+  alloc = kmm_malloc(size);
   if (alloc == NULL)
     {
       return -ENOMEM;

graphics/nxbe/nxbe_setsize.c

@@ -129,7 +129,7 @@ static void nxbe_realloc(FAR struct nxbe_window_s *wnd,
 #else
       /* Re-allocate memory from the user space heap. */
 
-      newfb = (FAR nxgl_mxpixel_t *)kumm_malloc(newfbsize);
+      newfb = kumm_malloc(newfbsize);
       if (newfb == NULL)
         {
           /* Fall back to no RAM back up */

graphics/nxmu/nxmu_kbdin.c

@@ -61,7 +61,7 @@ void nxmu_kbdin(FAR struct nxmu_state_s *nxmu, uint8_t nch, FAR uint8_t *ch)
    */
 
   size   = sizeof(struct nxclimsg_kbdin_s) + nch - 1;
-  outmsg = (FAR struct nxclimsg_kbdin_s *)kmm_malloc(size);
+  outmsg = kmm_malloc(size);
   if (outmsg)
     {
       /* Give the keypad input only to the top child */

graphics/nxmu/nxmu_openwindow.c

@@ -132,7 +132,7 @@ void nxmu_openwindow(FAR struct nxbe_state_s *be,
        *      levels.
        */
 
-      wnd->fbmem = (FAR nxgl_mxpixel_t *)kumm_malloc(fbsize);
+      wnd->fbmem = kumm_malloc(fbsize);
       if (wnd->fbmem == NULL)
         {
           /* Fall back to no RAM back up */