package/tinycbor: override prefix at build time as well

To ensure the correct prefix is used in the generated tinycbor.pc instead of
/usr/local:

>>> tinycbor 0.6.0 Building
..
sed > tinycbor.pc < tinycbor.pc.in \
        -e 's,@prefix@,/usr/local,' \
        -e 's,@exec_prefix@,/usr/local,' \
        -e 's,@libdir@,/usr/local/lib,' \
        -e 's,@includedir@,/usr/local/include,' \
        -e 's,@version@,0.6.0,'
>>> tinycbor 0.6.0 Installing to staging directory
..
install -m 644 tinycbor.pc /path/to/buildroot/output/host/aarch64-buildroot-linux-gnu/sysroot/usr/lib/pkgconfig/tinycbor.pc

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
(cherry picked from commit b059e084201108255db61a27824d4bb8159d1054)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/tinycbor/tinycbor.mk

@@ -16,7 +16,7 @@ ifeq ($(BR2_PACKAGE_CJSON),y)
 TINYCBOR_DEPENDENCIES += cjson
 endif
 
-TINYCBOR_MAKE_OPTS = $(TARGET_CONFIGURE_OPTS) DISABLE_WERROR=1 V=1
+TINYCBOR_MAKE_OPTS = $(TARGET_CONFIGURE_OPTS) DISABLE_WERROR=1 V=1 prefix=/usr
 
 ifeq ($(BR2_STATIC_LIBS),y)
 TINYCBOR_MAKE_OPTS += BUILD_STATIC=1 BUILD_SHARED=0
@@ -34,12 +34,12 @@ endef
 
 define TINYCBOR_INSTALL_STAGING_CMDS
 	$(TARGET_MAKE_ENV) $(MAKE) $(TINYCBOR_MAKE_OPTS) -C $(@D) \
-		DESTDIR=$(STAGING_DIR) prefix=/usr install
+		DESTDIR=$(STAGING_DIR) install
 endef
 
 define TINYCBOR_INSTALL_TARGET_CMDS
 	$(TARGET_MAKE_ENV) $(MAKE) $(TINYCBOR_MAKE_OPTS) -C $(@D) \
-		DESTDIR=$(TARGET_DIR) prefix=/usr install
+		DESTDIR=$(TARGET_DIR) install
 endef
 
 $(eval $(generic-package))