sha2: use size of struct and not of pointer in memset()

The size of the struct should be given here and not the size of the
pointer. clang pointed out this error.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
debug: remove unneeded check negative level

level is an enumeration and therefor never negative. Remove the
useless checks. clang pointed out this problem.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
debug: remove unneeded check negative compression

compression is an enumeration and therefor never negative. Remove the
useless checks. clang pointed out this problem.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>