asm-generic: uaccess: 1-byte access is always aligned

With the cleaned up version of asm-generic/unaligned.h,
there is a warning about the get_user/put_user helpers using
unaligned access for single-byte variables:

include/asm-generic/uaccess.h: In function ‘__get_user_fn’:
include/asm-generic/unaligned.h:13:15: warning: ‘packed’ attribute ignored for field of type ‘u8’ {aka ‘unsigned char’} [-Wattributes]
  const struct { type x __packed; } *__pptr = (typeof(__pptr))(ptr); \

Change these to use a direct pointer dereference to avoid the
warnings.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>