rt-tests: Fix warning flag typo

As per the comment, this makes it match the Makefile

(From OE-Core rev: 6fce92430e6e837d068eb8531dcd432f38adca3a)

(From OE-Core rev: be4aef60e6da08b77a5c1fbbf783305bee9f96ae)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-rt/rt-tests/rt-tests.inc

@@ -11,7 +11,7 @@ SRC_URI = "git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git
 S = "${WORKDIR}/git"
 
 # need to append rt-tests' default CFLAGS to ours
-CFLAGS += "-I${S}/src/include -D_GNU_SOURCE -Wall -Wno-nonnulli"
+CFLAGS += "-I${S}/src/include -D_GNU_SOURCE -Wall -Wno-nonnull"
 
 # calling 'uname -m' is broken on crossbuilds
 EXTRA_OEMAKE = "NUMA=0"