[ARM] 5177/1: arm/mach-sa1100/Makefile: remove CONFIG_SA1100_USB

This patch removes the commented out line for the not available
CONFIG_SA1100_USB option.

Reported-by: Robert P. J. Day <rpjday@crashcourse.ca>

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>