mpc8220/i2c.c: Fix GCC 4.6 build warning

Fix:
i2c.c: In function 'wait_for_bb':
i2c.c:109:16: warning: variable 'temp' set but not used
[-Wunused-but-set-variable]

Signed-off-by: Wolfgang Denk <wd@denx.de>
Cc: Heiko Schocher <hs@denx.de>