Fix incompatible function pointer types

[elig0n]

Fixes

[ 88%] Built target manpage
/tmp/yay-build/rofi-file-browser-extended-git/src/rofi-file-browser-extended/src/filebrowser.c:380:27: error: initialization of ‘cairo_surface_t * (*)(const Mode *, unsigned int,  unsigned int)’ {aka ‘struct _cairo_surface * (*)(const struct rofi_mode *, unsigned int,  unsigned int)’} from incompatible pointer type ‘cairo_surface_t * (*)(const Mode *, unsigned int,  int)’ {aka ‘struct _cairo_surface * (*)(const struct rofi_mode *, unsigned int,  int)’} [-Wincompatible-pointer-types]
  380 |     ._get_icon          = file_browser_get_icon,
      |                           ^~~~~~~~~~~~~~~~~~~~~
/tmp/yay-build/rofi-file-browser-extended-git/src/rofi-file-browser-extended/src/filebrowser.c:380:27: note: (near initialization for ‘mode._get_icon’)
make[2]: *** [CMakeFiles/filebrowser.dir/build.make:90: CMakeFiles/filebrowser.dir/src/filebrowser.c.o] Error 1