umh: simplify the capability pointer logic

The usermodehelper code uses two fake pointers for the two capability
cases: CAP_BSET for reading and writing 'usermodehelper_bset', and
CAP_PI to read and write 'usermodehelper_inheritable'.

This seems to be a completely unnecessary indirection, since we could
instead just use the pointers themselves, and never have to do any "if
this then that" kind of logic.

So just get rid of the fake pointer values, and use the real pointer
values instead.

Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Kees Cook <keescook@chromium.org>
Cc: Iurii Zaikin <yzaikin@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>