sh: fix trivial misannotations

Trivial misannotations in
* get_user() (__gu_addr is a userland pointer there)
* ip_fast_csum() (sum is __wsum, not unsigned int)
* csum_and_copy_to_user() (destination is void *, not const void * -
mea culpa)
* __clear_user() (to is a userland pointer)
* several places in kernel/traps_32.c (regs->pc is a userland pointer
when regs is a userland pt_regs)
* math-emu/math.c: READ() and WRITE() casts of address should be to
userland pointer.

No changes in code generation and those take care of the majority of
noise from sparse on sh builds.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Tested-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Signed-off-by: Rich Felker <dalias@libc.org>