linux/linux.mk: correct LINUX_ARCH_PATH for sparc64

Buildroot uses variable LINUX_ARCH_PATH to refer to the arch-specific
directory in the Linux tree, which may not necessarily be arch/$(KERNEL_ARCH).

Buildroot already accounts for the case of KERNEL_ARCH=i386 and
KERNEL_ARCH=x86_64, but does not for KERNEL_ARCH=sparc64, in which case the
correct directory is arch/sparc.

Reported-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Thomas De Schampheleire <thomas.de_schampheleire@nokia.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
(cherry picked from commit 0ecfdc093227c37ed1083e43404b748e8ee8a323)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

linux/linux.mk

@@ -237,6 +237,8 @@ ifeq ($(KERNEL_ARCH),i386)
 LINUX_ARCH_PATH = $(LINUX_DIR)/arch/x86
 else ifeq ($(KERNEL_ARCH),x86_64)
 LINUX_ARCH_PATH = $(LINUX_DIR)/arch/x86
+else ifeq ($(KERNEL_ARCH),sparc64)
+LINUX_ARCH_PATH = $(LINUX_DIR)/arch/sparc
 else
 LINUX_ARCH_PATH = $(LINUX_DIR)/arch/$(KERNEL_ARCH)
 endif