MIPS: Lasat: Fix build error if CRC32 is not enabled.

Kconfig doesn't select CRC32 so it's possible to build a Lasat kernel
without CONFIG_CRC32 resulting in a build error:

  LD      vmlinux
arch/mips/built-in.o: In function `lasat_init_board_info':
(.text+0x22c): undefined reference to `crc32_le'
arch/mips/built-in.o: In function `lasat_write_eeprom_info':
(.text+0x7fc): undefined reference to `crc32_le'
make: *** [vmlinux] Error 1

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>