src/Makefile.am: remove host headers incdlue

Using host headers is bad for cross compilation. Instead, use the '=' prefix
which expands to the current sysroot.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
---
diff -Nuar sdparm-1.09-orig/src/Makefile.am sdparm-1.09/src/Makefile.am
--- sdparm-1.09-orig/src/Makefile.am	2014-09-23 18:48:44.000000000 +0300
+++ sdparm-1.09/src/Makefile.am	2015-02-06 09:33:43.693477667 +0200
@@ -41,7 +41,7 @@
 			../lib/sg_pt_common.c
 
 if HAVE_SGUTILS
-INCLUDES = -I/usr/include/scsi
+INCLUDES = -I=/scsi
 sdparm_LDADD = @GETOPT_O_FILES@ @os_libs@ @SGUTILS_LIBS@
 sdparm_DEPENDENCIES = @GETOPT_O_FILES@
 else