asm-generic: mark __{get,put}_user_fn as __always_inline

Without the explicit __always_inline, some RISC-V configs place the
functions out of line, triggering the BUILD_BUG_ON checks in the
function.

Fixes: 11129e8e ("riscv: use memcpy based uaccess for nommu again")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>