[openwrt/openwrt] build: fix warnings from grep

[LEDE Commits]

ansuel pushed a commit to openwrt/openwrt.git, branch master:
https://git.openwrt.org/c5e167e0d6075c46ca92c30b425c4dcb05fec5ed

commit c5e167e0d6075c46ca92c30b425c4dcb05fec5ed
Author: Chris Osgood <chris_github at functionalfuture.com>
AuthorDate: Thu Sep 15 08:09:38 2022 -0400

    build: fix warnings from grep
    
    Fixes build warnings when using newer versions of grep.
    
    Signed-off-by: Chris Osgood <chris_github at functionalfuture.com>
    Tested-by: Georgi Valkov <gvalkov at gmail.com>
---
 target/sdk/files/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/target/sdk/files/Makefile b/target/sdk/files/Makefile
index f620f0ef01..dca8bbe20e 100644
--- a/target/sdk/files/Makefile
+++ b/target/sdk/files/Makefile
@@ -14,7 +14,7 @@ export TOPDIR LC_ALL LANG SDK
 
 world:
 
-DISTRO_PKG_CONFIG:=$(shell $(TOPDIR)/scripts/command_all.sh pkg-config | grep -E '\/usr' -m 1)
+DISTRO_PKG_CONFIG:=$(shell $(TOPDIR)/scripts/command_all.sh pkg-config | grep '/usr' -m 1)
 export PATH:=$(TOPDIR)/staging_dir/host/bin:$(PATH)
 
 ifneq ($(OPENWRT_BUILD),1)