usb: musb: remove incorrectly added ARCH_U5500 define

ARCH_U8500 covers both MACH_U8500 and MACH_U5500

Reported-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Mian Yousaf Kaukab <mian.yousaf.kaukab@stericsson.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>