AP_OSD: fixes for modified AP_ROMFS API

need to use AP_ROMFS::free()

libraries/AP_OSD/AP_OSD_MAX7456.cpp

@@ -161,7 +161,7 @@ bool AP_OSD_MAX7456::update_font()
     char fontname[] = "font0.bin";
     last_font = get_font_num();
     fontname[4] = last_font + '0';
-    uint8_t *font_data = AP_ROMFS::find_decompress(fontname, font_size);
+    const uint8_t *font_data = AP_ROMFS::find_decompress(fontname, font_size);
     if (font_data == nullptr || font_size != NVM_RAM_SIZE * 256) {
         return false;
     }
@@ -173,7 +173,7 @@ bool AP_OSD_MAX7456::update_font()
             //update char inside max7456 NVM
             if (!update_font_char(chr, chr_font_data)) {
                 hal.console->printf("AP_OSD: error during font char update\n");
-                free(font_data);
+                AP_ROMFS::free(font_data);
                 return false;
             }
             updated_chars++;
@@ -183,7 +183,7 @@ bool AP_OSD_MAX7456::update_font()
         hal.console->printf("AP_OSD: updated %d symbols.\n", updated_chars);
     }
     hal.console->printf("AP_OSD: osd font is up to date.\n");
-    free(font_data);
+    AP_ROMFS::free(font_data);
     return true;
 }
 

libraries/AP_OSD/AP_OSD_SITL.cpp

@@ -47,7 +47,7 @@ void AP_OSD_SITL::load_font(void)
     char fontname[] = "font0.bin";
     last_font = get_font_num();
     fontname[4] = last_font + '0';
-    uint8_t *font_data = AP_ROMFS::find_decompress(fontname, font_size);
+    const uint8_t *font_data = AP_ROMFS::find_decompress(fontname, font_size);
     if (font_data == nullptr && last_font != 0) {
         last_font = 0;
         fontname[4] = last_font + '0';
@@ -97,7 +97,7 @@ void AP_OSD_SITL::load_font(void)
         }
         font[i].update(pixels);
     }
-    free(font_data);
+    AP_ROMFS::free(font_data);
 }
 
 void AP_OSD_SITL::write(uint8_t x, uint8_t y, const char* text)