ext4: fix INCOMPAT feature codepoint reservation for INLINEDATA

In commit 9b90e5e0 I incorrectly reserved the wrong bit for
EXT4_FEATURE_INCOMPAT_INLINEDATA per the discussion on the linux-ext4
list on December 7, 2011.  The codepoint 0x2000 should be used for
EXT4_FEATURE_INCOMPAT_USE_META_CSUM, so INLINEDATA will be assigned
the value 0x8000.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>