Revert "dm cache: fix arm link errors with inline"

This reverts commit 43aeaa29.

Since commit 0bddd227 ("Documentation: update for gcc 4.9 requirement")
the minimum supported version of GCC is gcc-4.9. It's now safe to remove
this code.

Link: https://github.com/ClangBuiltLinux/linux/issues/427


Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>