lib/crc32: remove unneeded casts

Casts were added in commit 8f243af4 ("sections: fix const sections
for crc32 table") to cope with the tables not being const. They are no
longer required since commit f5e38b92 ("lib: crc32: constify crc32
lookup table").

Signed-off-by: Kevin Bracey <kevin@bracey.fi>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>