vsprintf: reduce code size by avoiding extra check

vsprintf: reduce code size by avoiding extra check

No functional change, just refactor the code so that it avoid checking
"if (hi)" two times in a sequence, taking advantage of previous check made.

It also reduces code size:
   text    data     bss     dec     hex filename
  15726       0       8   15734    3d76 vsprintf.o (ex lib/lib.a-BEFORE)
  15710       0       8   15718    3d66 vsprintf.o (ex lib/lib.a-AFTER)

Signed-off-by: André Goddard Rosa <[email protected]>
Acked-by: Frederic Weisbecker <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>