package/jitterentropy-library: ensure make command is continued across new line

package/jitterentropy-library: ensure make command is continued across new line

The first line of JITTERENTROPY_LIBRARY_BUILD_CMDS must end with "\" to
concatenate the two lines.

Fixes: build error
[...]
/usr/bin/make -j33 -C
/local/users/mmayer/buildroot/output/arm64/build/jitterentropy-library-2.2.0
/local/users/mmayer/buildroot/output/arm64/host/bin/aarch64-linux-gcc
-shared -Wl,-soname,libjitterentropy.so.2 -o libjitterentropy.so.2.2.0
jitterentropy-base.o  -Wl,-z,relro,-z,now  -lrt
/local/users/mmayer/buildroot/output/arm64/host/bin/aarch64-linux-ar
rcs libjitterentropy.a jitterentropy-base.o
jitterentropy
/bin/bash: jitterentropy: command not found

Signed-off-by: Markus Mayer <mmayer@broadcom.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>