Allow aic7xx firmware to be built from BK tree.

[Peter Chubb]

This patch removes the two generate files (that are also in the
distributed kernel) before attempting to regenerate them.

The real question is, why are there generated files distributed with
the kernel source?

(Patch against 2.5.16)

===== drivers/scsi/aic7xxx/Makefile 1.8 vs edited =====
--- 1.8/drivers/scsi/aic7xxx/Makefile   Thu Apr 25 05:16:44 2002
+++ edited/drivers/scsi/aic7xxx/Makefile        Tue May 14 10:04:50 2002
@@ -26,6 +26,7 @@
 
 ifeq ($(CONFIG_AIC7XXX_BUILD_FIRMWARE),y)
 aic7xxx_seq.h aic7xxx_reg.h: aic7xxx.seq aic7xxx.reg aicasm/aicasm
+       -rm -f aic7xx_seq.h aic7xx_reg.h
        aicasm/aicasm -I. -r aic7xxx_reg.h -o aic7xxx_seq.h aic7xxx.seq
 endif