GCC4.6: Squash warnings in lcd.c

lcd.c: In function ‘lcd_drawchars’:
lcd.c:214:9: warning: variable ‘off’ set but not used
[-Wunused-but-set-variable]
lcd.c: In function ‘lcd_display_bitmap’:
lcd.c:617:16: warning: variable ‘compression’ set but not used
[-Wunused-but-set-variable]

Signed-off-by: Marek Vasut <marek.vasut@gmail.com>