fs/erofs: unbreak custom compression handling

Fixes:
https://autobuild.buildroot.net/results/0f856def945b9a863f45f7a58553b62f6875720b/

Commit a02e43741719 ("fs/erofs: add custom compression option with optional
compress-hints file") added logic for custom compression, but in fact it did
not work.

BR2_TARGET_ROOTFS_EROFS_COMPRESSION_{ALGORITHMS,HINTS} are kconfig string
variables, so we need to use qstrip rather than strip.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Arnout Vandecappelle <arnout@rnout.be>
(cherry picked from commit 585eeb464018f2c5865b71251df83e10a02cb8b0)
Signed-off-by: Thomas Perale <thomas.perale@mind.be>

fs/erofs/erofs.mk

@@ -11,9 +11,9 @@ ROOTFS_EROFS_ARGS += -zlz4hc,$(BR2_TARGET_ROOTFS_EROFS_LZ4HC_LEVEL)
 else ifeq ($(BR2_TARGET_ROOTFS_EROFS_LZMA),y)
 ROOTFS_EROFS_ARGS += -zlzma,$(BR2_TARGET_ROOTFS_EROFS_LZMA_LEVEL)
 else ifeq ($(BR2_TARGET_ROOTFS_EROFS_CUSTOM_COMPRESSION),y)
-ROOTFS_EROFS_ARGS += -z$(strip $(BR2_TARGET_ROOTFS_EROFS_COMPRESSION_ALGORITHMS))
-ifneq ($(strip $(BR2_TARGET_ROOTFS_EROFS_COMPRESSION_HINTS)),)
-ROOTFS_EROFS_ARGS += --compress-hints $(strip $(BR2_TARGET_ROOTFS_EROFS_COMPRESSION_HINTS))
+ROOTFS_EROFS_ARGS += -z$(call qstrip,$(BR2_TARGET_ROOTFS_EROFS_COMPRESSION_ALGORITHMS))
+ifneq ($(call qstrip,$(BR2_TARGET_ROOTFS_EROFS_COMPRESSION_HINTS)),)
+ROOTFS_EROFS_ARGS += --compress-hints $(call qstrip,$(BR2_TARGET_ROOTFS_EROFS_COMPRESSION_HINTS))
 endif
 endif