fix a braino in "sparc32: fix register window handling in genregs32_[gs]et()"

lost npc in PTRACE_SETREGSET, breaking PTRACE_SETREGS as well

Fixes: cf51e129 "sparc32: fix register window handling in genregs32_[gs]et()"
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>