style and compilation fixes for src/enjoy.c

[maribu]

• drop same trailing whitespace in src/enjoy.c
• consistently use 4 spaces for indent (replace some instances where 3 spaces were used instead)
• fix incorrect use of printf format specifier to fix

enjoy.c:413:55: warning: format '%ld' expects argument of type 'long int', but argument 3 has type 'size_t' {aka 'unsigned int'} [-Wformat=]
  413 |                     sprintf(axis_as_mouse_key, "axis%ld_as_mouse", axis);
      |                                                     ~~^            ~~~~
      |                                                       |            |
      |                                                       long int     size_t {aka unsigned int}
      |                                                     %d