Fix ixp4xx compile error

Fix ixp4xx compile error

drivers/input/misc/ixp4xx-beeper.c: In function 'ixp4xx_spkr_event':
drivers/input/misc/ixp4xx-beeper.c:54: error: 'input_dev' undeclared (first use in this function)
drivers/input/misc/ixp4xx-beeper.c:54: error: (Each undeclared identifier is reported only once
drivers/input/misc/ixp4xx-beeper.c:54: error: for each function it appears in.)

Signed-off-by: Frederik Deweerdt <[email protected]>
Acked-by: Dmitry Torokhov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>