genunifont: avoid format-security compiler warning

genunifont: avoid format-security compiler warning

Current warning without the patch:
src/genunifont.c: In function 'print_data_row':
src/genunifont.c:85:3: warning: format not a string literal and no format arguments [-Wformat-security]
src/genunifont.c:88:3: warning: format not a string literal and no format arguments [-Wformat-security]

We use fputs() to avoid any format-string parsing and instead directly
write the string into the file.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>