generic: refresh the LoongArch vDSO prefix map patch

The patch ends in an empty line where quilt writes a context line
holding a single space, so `make target/linux/refresh` rewrites it
and the kernel patch check fails on every target.

Fixes: 115209aa22 ("kernel: make the LoongArch vDSO build id independent of the build path")
Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Julius Bairaktaris <julius@bairaktaris.de>
Link: https://github.com/openwrt/openwrt/pull/25333
Signed-off-by: Jonas Jelonek <jonas@jonasjelonek.de>

target/linux/generic/pending-6.12/304-LoongArch-vdso-keep-the-prefix-map-flags.patch

@@ -40,4 +40,4 @@ Signed-off-by: John Crispin <john@phrozen.org>
 +	$(filter -fdebug-prefix-map=%,$(KBUILD_CFLAGS)) \
  	$(CLANG_FLAGS) \
  	-D__VDSO__
-
+ 

target/linux/generic/pending-6.18/304-LoongArch-vdso-keep-the-prefix-map-flags.patch

@@ -40,4 +40,4 @@ Signed-off-by: John Crispin <john@phrozen.org>
 +	$(filter -fdebug-prefix-map=%,$(KBUILD_CFLAGS)) \
  	$(CLANG_FLAGS) \
  	-D__VDSO__
-
+