arch/sh/boards/mach-dreamcast/irq.c: Remove duplicate header

arch/sh/boards/mach-dreamcast/irq.c: Remove duplicate header

Remove linux/irq.h which is included more than once.

Link: http://lkml.kernel.org/r/5c8682ef.1c69fb81.5a1ea.2e7f@mx.google.com
Signed-off-by: Sabyasachi Gupta <sabyasachi.linux@gmail.com>
Acked-by: Souptick Joarder <jrdr.linux@gmail.com>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Rich Felker <dalias@libc.org>
Cc: Mukesh Ojha <mojha@codeaurora.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>