microblaze: fix kbuild redundant file warning

Fix build warning since this file is already listed in
include/asm-generic/Kbuild.

../scripts/Makefile.asm-generic:25: redundant generic-y found in arch/microblaze/include/asm/Kbuild: hw_irq.h

Fixes: 630f289b ("asm-generic: make more kernel-space headers mandatory")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Michal Simek <michal.simek@xilinx.com>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Masahiro Yamada <masahiroy@kernel.org>
Link: https://lore.kernel.org/r/4d992aee-8a69-1769-e622-8d6d6e316346@infradead.org


Signed-off-by: Michal Simek <michal.simek@xilinx.com>