CSKY: Fix special_function in howto table

The special_function for reloc should be 'bfd_elf_generic_reloc',
reloc list:
	R_CKCORE_PCREL_IMM16BY2,
	R_CKCORE_PCREL_IMM16BY4,
	R_CKCORE_PCREL_IMM10BY4,
	R_CKCORE_PCREL_IMM18BY2,
	R_CKCORE_PCREL_FLRW_IMM8BY4

bfd/
	* elf32-csky.c (csky_elf_howto_table)
	<R_CKCORE_PCREL_IMM16BY2>: Set special_function to
	bfd_elf_generic_reloc.
	<R_CKCORE_PCREL_IMM16BY4>: Likewise.
	<R_CKCORE_PCREL_IMM10BY4>: Likewise.
	<R_CKCORE_PCREL_IMM18BY2>: Likewise.
	<R_CKCORE_PCREL_FLRW_IMM8BY4>: Likewise.