staging: android: logger: simplify and optimize get_entry_len

Make this code slightly easier to read, and eliminate calls
to sub-routines.  Some of these were previously optimized away
by the compiler, but one memcpy was not.

In my testing, this makes the code about 20% smaller, and
has no sub-routine calls and no branches (on ARM).

v2 of this patch is, IMHO, easier to read than v1. Compared to
that patch it uses __u8 instead of unsigned char, for
consistency with the __u16 val data type, simplifies the
conditional expression, adds a another comment, and
moves a common statement out of the if.

Signed-off-by: Tim Bird <tim.bird@am.sony.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>